discussion: Add a documentation site

[KennethEnevoldsen]

It seems like mteb has grown big enough now to warrant a documentation site. We already have a decent amount of the documentation written, but it is not too easy to find.

This issue is mostly to start the discussion or for people to add a thumbs up if they would like more documentation. It also adds a place for people to write what they would want from the docs.

[isaac-chung]

Should we convert this into a discussion?