Updates to main readme to remove top image and add call outs for plug…

…-ins (microsoft#1155)

### Motivation and Context
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  1. Why is this change required? Removed outdates top image
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### Description
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N/A

### Contribution Checklist
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- [x] The code builds clean without any errors or warnings
- [x] The PR follows SK Contribution Guidelines
(https://github.com/microsoft/semantic-kernel/blob/main/CONTRIBUTING.md)
- [x] The code follows the .NET coding conventions
(https://learn.microsoft.com/dotnet/csharp/fundamentals/coding-style/coding-conventions)
verified with `dotnet format`
- [x] All unit tests pass, and I have added new tests where possible
- [x] I didn't break anyone 😄

---------

Co-authored-by: Harleen Thind <39630244+hathind-ms@users.noreply.github.com>

README.md

@@ -27,11 +27,8 @@ chaining,
 [intelligent planning](docs/PLANNERS.md)
 capabilities out of the box.
 
-![image](https://user-images.githubusercontent.com/371009/221739773-cf43522f-c1e4-42f2-b73d-5ba84e21febb.png)
-
 Semantic Kernel supports and encapsulates several design patterns from the latest
-in AI research, such that developers can infuse their applications with complex
-[skills](docs/SKILLS.md) like [prompt](docs/PROMPT_TEMPLATE_LANGUAGE.md)
+in AI research, such that developers can infuse their applications with  [plugins](https://learn.microsoft.com/semantic-kernel/howto/) like [prompt](docs/PROMPT_TEMPLATE_LANGUAGE.md)
 chaining, recursive reasoning, summarization, zero/few-shot learning, contextual
 memory, long-term memory, [embeddings](docs/EMBEDDINGS.md), semantic indexing,
 [planning](docs/PLANNERS.md), retrieval-augmented generation and accessing external
@@ -87,7 +84,7 @@ Follow the links for more information and instructions about running these apps.
 
 |                                                                         |                                                                                                                                   |
 | ----------------------------------------------------------------------- | --------------------------------------------------------------------------------------------------------------------------------- |
-| [Simple chat summary](samples/apps/chat-summary-webapp-react/README.md) | Use ready-to-use skills and get those skills into your app easily.                                                                |
+| [Simple chat summary](samples/apps/chat-summary-webapp-react/README.md) | Use ready-to-use plugins and get plugins into your app easily.                                                                |
 | [Book creator](samples/apps/book-creator-webapp-react/README.md)        | Use planner to deconstruct a complex goal and envision using the planner in your app.                                             |
 | [Authentication and APIs](samples/apps/auth-api-webapp-react/README.md) | Use a basic connector pattern to authenticate and connect to an API and imagine integrating external data into your app's LLM AI. |
 | [GitHub repository Q&A](samples/apps/github-qna-webapp-react/README.md) | Use embeddings and memory to store recent data and allow you to query against it.                                                 |