docs: update README.

[thruflo]

Update the readme to better describe / reflect what the library is. Adds an FAQ section and aligns better with the README structure and furniture of other TanStack libraries.

Initial usage docs in ./docs/index.md. There's more to flesh out there but I believe the update tracks the latest changes. I've included QueryCollection because I assume we're merging #62 soon.

https://github.com/TanStack/db/blob/thruflo/readme/README.md

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[KyleAMathews]

Looking great!

[thruflo]

@samwillis perhaps there's more you'd like to add here?

For example, the non-hook query interface? Also I think the "it's collections all the way down" concept is powerful, i.e.: that queries can be composed. Perhaps we can surface that in the usage docs here?

[KyleAMathews]

Yeah, it's very powerful and unique.

Two examples I've liked of the creating materialized views for easier querying in the app and cloning a collection to scope optimistic updates to part of the app.

[thruflo]

How about we merge this and improve in subsequent PRs?

[samwillis]

Yep, let's do that.

I need to add a bunch of docs for the query builder - I'll try and get on to that today.