Add LLM topic

[Sergyenko]

Please confirm this pull request meets the following requirements:

• I followed the contributing guidelines: https://github.com/github/explore/blob/main/CONTRIBUTING.md.
• I am not the sole author or employee of a company who created either the topic I am modifying/adding or the collection entry I am modifying/adding.

Which change are you proposing?

• Suggesting edits to an existing topic or collection
• Curating a new topic or collection
• Something that does not neatly fit into the binary options above

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Curating a new topic or collection

• I've formatted my changes as a new folder directory, named for the topic or collection as it appears in the URL on GitHub (e.g. https://github.com/topics/[NAME] or https://github.com/collections/[NAME])
• My folder contains a *.png image (if applicable) and index.md
• All required fields in my index.md conform to the Style Guide and API docs: https://github.com/github/explore/tree/main/docs

I believe more and more software engineers are getting into work related to LLMs (Large language models), so I hope this topic will be beneficial for community of developers and AI enthusiasts.

So I've added initial description for the whole LLM topic and will add more related content as it appears.

[Sergyenko]

I'm sorry, please let me know how I can fix that issue about Topic PR Commenter?

[ahpook]

LGTM, I'm not wild about the graphic but it's fine. Kind of surprised there is not already a curated topic for this! Thanks @Sergyenko !

[ahpook]

@Sergyenko that test is bad, don't worry about it. Merging.