README rewrite

[tjburch]

Overhaul README to be somewhat less verbose and to-the-point. Aimed to reduce the number of full dataframe printouts we had, raise the full docs folder to be more visible. Some notes:

• Removed the version number. It's on git, so it should be clear by the sidebar
• Removed the changelog link. Git has an internal changelog that we seem to be better about using.
• I think it makes sense for contributing.md to be a contributing guide rather than suggestions on things to add. So I wrote it as if that's the future paradigm. We'll need to update contributing.md correspondingly.

Has the discord link so supersedes #292. I'll take that one down.

[schorrm]

LGTM in general, I would put the discord link at the top though