[Tutorials] Add LPython tutorial 1

tutorial/tutorial_1.md

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+# LPython Tutorial: 1
+
+This is the first tutorial of LPython compiler.
+
+## Installation
+
+Please follow the steps mentioned in the
+[LPython's installation instructions](https://github.com/lcompilers/lpython#installation).
+
+After installation, verify it using:
+```
+% lpython --version
+LPython version: 0.20.0
+Platform: macOS ARM
+Default target: arm64-apple-darwin22.1.0
+```
+
+
+## Getting started with lpython
+
+Let's begin by compiling the very first code example using `lpython`.
+Copy the contents of `hello.py`.
+
+```
+% cat hello.py
+def main():
+    print("Hello LPython!")
+
+main()
+```
+
+Compile and run it using:
+
+```
+% lpython hello.py
+Hello LPython!
+```
+
+`lpython` is designed to work exactly in the same way as `python`. LPython
+is designed such that it is the **subset** of CPython and with the aim of
+whatever works in LPython should also work in CPython!
+
+Now, if we want to compile and run separately, we can do:
+
+```
+% lpython hello.py -o hello.out # just compile it!
+% ./hello.out # run the binary!
+Hello LPython!
+```
+
+### Variables
+
+LPython is a strictly typed python compiler, meaning, each variable must
+have a type just like C, or C++. Some of the basic supported types are
+
+| Types    | Description |
+| -------- | ------- |
+| i1, i8, i16, i32, i64  | Integer type supporting 1, 8, 16, 32, and 64 bits |
+| u8, u16, u32, u64 | Unsigned Integer type supporting 8, 16, 32, and 64 bits |
+| str | String type|
+| bool | Boolean type |
+| f32, f64    | Real type supporting 32 and 64 bits  |
+| c32, c64    | Real type supporting 32 and 64 bits |
+| CPtr | C Pointer type |
+| Const[T] | Constant type |
+| Callable| Callable type |
+| Allocatable | Allocatable type |
+| Pointer | Pointer type |
+| S | Symbolic type |
+
+Try the following variable example
+```
+% cat var1.py
+from lpython import i32, i64
+
+def variable_function_1():
+    x: i32 = 1
+    y: i32 = 2
+    print("x + y is", x + y)
+
+    x1: i64 = i64(10)
+    y1: i64 = i64(20)
+    print("x1 + y1 is", x1 + y1)
+
+variable_function_1()
+```
+
+Compile and run it
+
+```
+% lpython var1.py
+x + y is 3
+x1 + y1 is 30
+```
+
+Note that while instantiating `x1`, we have to **explicit casting** as
+default integer type in LPython is `i32`. Implicit casting is
+not supported to avoid any magic happening in your code and easy debugging.
+Look at the nice error thrown below if we haven't added explicit cast.
+
+```
+% cat var2.py
+from lpython import i32, i64
+
+def variable_function_error_1():
+    x1: i64 = 10
+    y1: i64 = 20
+    print("x1 + y1 is", x1 + y1)
+
+variable_function_error_1()
+```
+
+Compile and try to run it
+```
+% lpython var2.py
+semantic error: Type mismatch in annotation-assignment, the types must be compatible
+ --> var2.py:4:5
+  |
+4 |     x1: i64 = 10
+  |     ^^        ^^ type mismatch ('i64' and 'i32')
+
+
+Note: Please report unclear or confusing messages as bugs at
+https://github.com/lcompilers/lpython/issues.
+```
+
+Similarly, please note that the default type of float is `f64`.
+
+### Functions
+
+Functions in LPython are also strictly typed, meaning, each function
+argument should have a type. The function also needs to have a return
+type (if it returns a value).
+
+Consider the following example of how function looks
+```
+% cat func1.py
+from lpython import i32
+
+def function_void_example():
+    print("This function has no args and return type.")
+
+def function_with_args_and_ret(a: i32) -> i32:
+    # Function having i32 as return type
+    return a + 1
+
+def function_with_args(a: i32, b: str):
+    print("Hello", b)
+    c: i32 = function_with_args_and_ret(a)
+    print("You just got", c)
+
+function_void_example()
+function_with_args(2, "lpython")
+```
+
+Running this we get
+
+```
+% lpython func1.py
+This function has no args and return type.
+Hello lpython
+You just got 3
+```
+
+### Loops
+
+LPython provide loop in the same way as in python. The only extra
+condition is that the loop variable must be a typed and declared
+beforehand. Take a look at the `for` loop example to understand it better
+
+```
+% cat loop1.py
+from lpython import i32, i64
+
+def loop_for():
+    i: i32
+    res: i64 = i64(0)
+    for i in range(0, 10000):
+        res += i64(i)
+    print("for loop result:", res)
+
+def loop_while():
+    i: i32 = 1
+    res: i64 = i64(0)
+    while i < 10000:
+        res += i64(i)
+        i += 1
+    print("while loop result:", res)
+
+loop_for()
+loop_while()
+```