Add transformers-like api doc (#2018)

Signed-off-by: Kaihui-intel <kaihui.tang@intel.com>

docs/source/3x/transformers_like_api.md

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+Transformers-like API
+=====
+
+1. [Introduction](#introduction)
+
+2. [Supported Algorithms](#supported-algorithms)
+
+3. [Usage For Intel CPU](#usage-for-cpu)
+
+4. [Usage For Intel GPU](#usage-for-intel-gpu)
+
+5. [Examples](#examples)
+
+## Introduction
+
+Transformers-like API provides a seamless user experience of model compressions on Transformer-based models by extending Hugging Face transformers APIs, leveraging neural compressor existing weight-only quantization capability and replacing Linear operator with Intel® Extension for PyTorch.
+
+## Supported Algorithms
+
+| Support Device |  RTN  |  AWQ  |  TEQ |  GPTQ  | AutoRound |
+|:--------------:|:----------:|:----------:|:----------:|:----:|:----:|
+|     Intel CPU        |  ✔  |  ✔  |  ✔  |  ✔  |  ✔  |
+|     Intel GPU        |  ✔  |  stay tuned  |  stay tuned  |  ✔  |  ✔  |
+
+> Please refer to [weight-only quantization document](./PT_WeightOnlyQuant.md) for more details.
+
+
+## Usage For CPU 
+
+Our motivation is to improve CPU support for weight only quantization. We have extended the `from_pretrained` function so that `quantization_config` can accept [`RtnConfig`](https://github.com/intel/neural-compressor/blob/master/neural_compressor/transformers/utils/quantization_config.py#L243), [`AwqConfig`](https://github.com/intel/neural-compressor/blob/72398b69334d90cdd7664ac12a025cd36695b55c/neural_compressor/transformers/utils/quantization_config.py#L394), [`TeqConfig`](https://github.com/intel/neural-compressor/blob/72398b69334d90cdd7664ac12a025cd36695b55c/neural_compressor/transformers/utils/quantization_config.py#L464), [`GPTQConfig`](https://github.com/intel/neural-compressor/blob/72398b69334d90cdd7664ac12a025cd36695b55c/neural_compressor/transformers/utils/quantization_config.py#L298), [`AutoroundConfig`](https://github.com/intel/neural-compressor/blob/72398b69334d90cdd7664ac12a025cd36695b55c/neural_compressor/transformers/utils/quantization_config.py#L527) to implements conversion on the CPU.
+
+### Usage examples for CPU device
+quantization and inference with `RtnConfig`, `AwqConfig`, `TeqConfig`, `GPTQConfig`, `AutoRoundConfig` on CPU device.
+```python
+# RTN
+from neural_compressor.transformers import AutoModelForCausalLM, RtnConfig
+
+model_name_or_path = "MODEL_NAME_OR_PATH"
+woq_config = RtnConfig(bits=4)
+q_model = AutoModelForCausalLM.from_pretrained(
+    model_name_or_path,
+    quantization_config=woq_config,
+)
+
+# AWQ
+from neural_compressor.transformers import AutoModelForCausalLM, AwqConfig
+
+model_name_or_path = "MODEL_NAME_OR_PATH"
+woq_config = AwqConfig(bits=4)
+q_model = AutoModelForCausalLM.from_pretrained(
+    model_name_or_path,
+    quantization_config=woq_config,
+)
+
+# TEQ
+from transformers import AutoTokenizer
+from neural_compressor.transformers import AutoModelForCausalLM, TeqConfig
+
+model_name_or_path = "MODEL_NAME_OR_PATH"
+tokenizer = AutoTokenizer.from_pretrained(model_name_or_path)
+woq_config = TeqConfig(bits=4, tokenizer=tokenizer)
+q_model = AutoModelForCausalLM.from_pretrained(
+    model_name_or_path,
+    quantization_config=woq_config,
+)
+
+# GPTQ
+from transformers import AutoTokenizer
+from neural_compressor.transformers import AutoModelForCausalLM, GPTQConfig
+
+model_name_or_path = "MODEL_NAME_OR_PATH"
+tokenizer = AutoTokenizer.from_pretrained(model_name_or_path)
+woq_config = GPTQConfig(bits=4, tokenizer=tokenizer)
+woq_model = AutoModelForCausalLM.from_pretrained(
+    model_name_or_path,
+    quantization_config=woq_config,
+)
+
+# AutoRound
+from transformers import AutoTokenizer
+from neural_compressor.transformers import AutoModelForCausalLM, AutoRoundConfig
+
+model_name_or_path = "MODEL_NAME_OR_PATH"
+tokenizer = AutoTokenizer.from_pretrained(model_name_or_path)
+woq_config = AutoRoundConfig(bits=4, tokenizer=tokenizer)
+woq_model = AutoModelForCausalLM.from_pretrained(
+    model_name_or_path,
+    quantization_config=woq_config,
+)
+
+# inference
+from transformers import AutoTokenizer
+
+prompt = "Once upon a time, a little girl"
+tokenizer = AutoTokenizer.from_pretrained(model_name_or_path)
+
+input_ids = tokenizer(prompt, return_tensors="pt")["input_ids"]
+generate_kwargs = dict(do_sample=False, temperature=0.9, num_beams=4)
+gen_ids = q_model.generate(input_ids, **generate_kwargs)
+gen_text = tokenizer.batch_decode(gen_ids, skip_special_tokens=True)
+print(gen_text)
+```
+
+You can also save and load your quantized low bit model by the below code.
+
+```python
+# quant
+from neural_compressor.transformers import AutoModelForCausalLM, RtnConfig
+
+model_name_or_path = "MODEL_NAME_OR_PATH"
+woq_config = RtnConfig(bits=4)
+q_model = AutoModelForCausalLM.from_pretrained(
+    model_name_or_path,
+    quantization_config=woq_config,
+)
+
+# save quant model
+saved_dir = "SAVE_DIR"
+q_model.save_pretrained(saved_dir)
+
+# load quant model
+loaded_model = AutoModelForCausalLM.from_pretrained(saved_dir)
+```
+
+## Usage For Intel GPU
+Intel® Neural Compressor implement weight-only quantization for Intel GPU,(PVC/ARC/MTL/LNL) with [intel-extension-for-pytorch](https://github.com/intel/intel-extension-for-pytorch).
+
+Now 4-bit/8-bit inference with `RtnConfig`, `GPTQConfig`, `AutoRoundConfig` are support on Intel GPU device.
+
+We support experimental woq inference on Intel GPU,(PVC/ARC/MTL/LNL) with replacing Linear op in PyTorch. Validated models: meta-llama/Meta-Llama-3-8B, meta/llama-Llama-2-7b-hf, Qwen/Qwen-7B-Chat, microsoft/Phi-3-mini-4k-instruct.
+
+Here are the example codes.
+
+#### Prepare Dependency Packages
+1. Install Oneapi Package  
+The Oneapi DPCPP compiler is required to compile intel-extension-for-pytorch. Please follow [the link](https://www.intel.com/content/www/us/en/developer/articles/guide/installation-guide-for-oneapi-toolkits.html) to install the OneAPI to "/opt/intel folder".
+
+2. Build and Install PyTorch and intel-extension-for-pytorch. Please follow [the link](https://intel.github.io/intel-extension-for-pytorch/index.html#installation).
+
+3. Quantization Model and Inference
+```python
+import intel_extension_for_pytorch as ipex
+from neural_compressor.transformers import AutoModelForCausalLM
+from transformers import AutoTokenizer
+import torch
+
+model_name_or_path = "Qwen/Qwen-7B-Chat"  # MODEL_NAME_OR_PATH
+prompt = "Once upon a time, a little girl"
+input_ids = tokenizer(prompt, return_tensors="pt")["input_ids"]
+tokenizer = AutoTokenizer.from_pretrained(model_name_or_path, trust_remote_code=True)
+
+q_model = AutoModelForCausalLM.from_pretrained(model_name_or_path, device_map="xpu", trust_remote_code=True)
+
+# optimize the model with ipex, it will improve performance.
+quantization_config = q_model.quantization_config if hasattr(q_model, "quantization_config") else None
+q_model = ipex.optimize_transformers(
+    q_model, inplace=True, dtype=torch.float16, quantization_config=quantizaiton_config, device="xpu"
+)
+
+output = q_model.generate(input_ids, max_new_tokens=100, do_sample=True)
+print(tokenizer.batch_decode(output, skip_special_tokens=True))
+```
+
+> Note: If your device memory is not enough, please quantize and save the model first, then rerun the example with loading the model as below, If your device memory is enough, skip below instruction, just quantization and inference.
+
+4. Saving and Loading quantized model
+ * First step: Quantize and save model
+```python
+from neural_compressor.transformers import AutoModelForCausalLM, RtnConfig
+
+model_name_or_path = "MODEL_NAME_OR_PATH"
+woq_config = RtnConfig(bits=4)
+q_model = AutoModelForCausalLM.from_pretrained(
+    model_name_or_path, quantization_config=woq_config, device_map="xpu", trust_remote_code=True，
+)
+
+# Please note, saving model should be executed before ipex.optimize_transformers function is called.
+q_model.save_pretrained("saved_dir")
+```
+ * Second step: Load model and inference(In order to reduce memory usage, you may need to end the quantize process and rerun the script to load the model.)
+```python
+# Load model
+loaded_model = AutoModelForCausalLM.from_pretrained("saved_dir", trust_remote_code=True)
+
+# Before executed the loaded model, you can call ipex.optimize_transformers function.
+quantization_config = q_model.quantization_config if hasattr(q_model, "quantization_config") else None
+loaded_model = ipex.optimize_transformers(
+    loaded_model, inplace=True, dtype=torch.float16, quantization_config=quantization_config, device="xpu"
+)
+
+# inference
+from transformers import AutoTokenizer
+
+prompt = "Once upon a time, a little girl"
+tokenizer = AutoTokenizer.from_pretrained(model_name_or_path)
+input_ids = tokenizer(prompt, return_tensors="pt")["input_ids"]
+generate_kwargs = dict(do_sample=False, temperature=0.9, num_beams=4)
+gen_ids = loaded_model.generate(input_ids, **generate_kwargs)
+gen_text = tokenizer.batch_decode(gen_ids, skip_special_tokens=True)
+print(gen_text)
+```
+
+5. You can directly use [example script](https://github.com/intel/neural-compressor/blob/master/examples/3.x_api/pytorch/nlp/huggingface_models/language-modeling/quantization/transformers/weight_only/text-generation/run_generation_gpu_woq.py)
+```bash
+python run_generation_gpu_woq.py --woq --benchmark --model save_dir
+```
+
+>Note:
+> * Saving quantized model should be executed before the optimize_transformers function is called.
+> * The optimize_transformers function is designed to optimize transformer-based models within frontend Python modules, with a particular focus on Large Language Models (LLMs). It provides optimizations for both model-wise and content-generation-wise. The detail of `optimize_transformers`, please refer to [the link](https://github.com/intel/intel-extension-for-pytorch/blob/xpu-main/docs/tutorials/llm/llm_optimize_transformers.md).
+
+## Examples
+
+Users can also refer to [examples](https://github.com/intel/neural-compressor/blob/master/examples/3.x_api/pytorch/nlp/huggingface_models/language-modeling/quantization/transformers/weight_only/text-generation) on how to quantize a model with transformers-like api.