Suggestion: Add LLMs.txt for AutoGen Documentation Guides

[cc0zh]

Hello AutoGen Team,
I hope this message finds you well.
I'd like to suggest adding an LLMs.txt file specifically for the AutoGen user guide documentation hosted at https://microsoft.github.io/autogen/stable/user-guide/.
An LLMs.txt file can provide valuable directives for large language models (LLMs) and AI agents interacting with the documentation. This guidance could include preferred crawl paths, sections suitable for summarization, disallowed areas, citation preferences, etc.

[ekzhu]

Sounds like a great idea. Issue: #6271