Update discover.md with adding email agent package (#6274)

adding email agent

## Why are these changes needed?

This PR introduces an AI-powered email assistant that can generate
images, attach files, draft reports, and send emails to multiple
recipients or specific users based on their queries. This feature is
highly beneficial for customer management and email marketing, enhancing
automation and improving efficiency.

## Related issue number

Open #6228 
## Checks

- [x] I've included any doc changes needed for
<https://microsoft.github.io/autogen/>. See
<https://github.com/microsoft/autogen/blob/main/CONTRIBUTING.md> to
build and test documentation locally.
- [x] I've added tests (if relevant) corresponding to the changes
introduced in this PR.
- [x] I've made sure all auto checks have passed.

python/packages/autogen-core/docs/src/user-guide/extensions-user-guide/discover.md

@@ -42,6 +42,7 @@ Find community samples and examples of how to use AutoGen
 | [autogen-watsonx-client](https://github.com/tsinggggg/autogen-watsonx-client)  | [PyPi](https://pypi.org/project/autogen-watsonx-client/) | Model client for [IBM watsonx.ai](https://www.ibm.com/products/watsonx-ai) |
 | [autogen-openaiext-client](https://github.com/vballoli/autogen-openaiext-client)  | [PyPi](https://pypi.org/project/autogen-openaiext-client/) | Model client for other LLMs like Gemini, etc. through the OpenAI API |
 | [autogen-ext-mcp](https://github.com/richard-gyiko/autogen-ext-mcp) | [PyPi](https://pypi.org/project/autogen-ext-mcp/) | Tool adapter for Model Context Protocol server tools |
+| [autogen-ext-email](https://github.com/masquerlin/autogen-ext-email) | [PyPi](https://pypi.org/project/autogen-ext-email/) | A Email agent for generating email and sending |
 
 <!-- Example -->
 <!-- | [My Model Client](https://github.com/example)  | [PyPi](https://pypi.org/project/example) | Model client for my custom model service | -->