Add user-focused documentation

[alexkreidler]

It would be great to have a user guide in the style of the Rust book or https://ballistacompute.org/docs/introduction.html, beyond what the API docs and examples provide.

[alexkreidler]

It would also be great to have some higher-level architecture docs describing the various internal components.

Also, it would be very helpful to list which features are supported out of these: https://ballistacompute.org/docs/reference.html.

In Rustdoc I see a whole list including Filter, LeftJoin, InnerJoin and more, but I'm not sure if those are fully implemented/supported yet.

Thanks to all for your hard work!

[alecmocatta]

Thanks for checking out the project @alexkreidler!

Totally agree, Amadeus could really do with some user-oriented docs. And some docs, period :)

I've just got back from holiday and have stome stuff to catch up on but I'll work on this in the next couple weeks.