[Docs] useMatches documentation

[ryanleichty]

I was trying to better understand the use case for useMatches and the Algolia search results were a bit limited in what was surfaced. I eventually found a few other pages that were of more help that might be relevant to reference on this page:

• https://reactrouter.com/how-to/using-handle
• https://reactrouter.com/6.30.4/hooks/use-matches (old docs, but included even more relevant info)

My LLM buddies were of course helpful, but still nice having detailed docs to fallback on!

[brophdawg11]

I'm going to convert this to a bug since I agree this should be surfaced better. Would be happy to accept a PR!