README clean up

[kpgalligan]

The README is old and has a lot in it. I think it can be cleaned up:

Manually installing and updating the plugin can go in a different doc. The README should assume you're using the cli.

The "sources" discussion, and anything related to that can go in a different doc. I don't want to hide our roots, but main README should be pretty clean.

Same with "Future Stuff"

I think the update/repair should go right after install. Sort of go through the tool first, then go through using the plugin. There's a conflict there. What would the user likely do first vs keeping related topics together? Because the process of adding source is a little tricky, I think that needs to be expanded. The section on the cli can be shorter, so we can at least do install and repair in one block.

There's another ticket #65 for videos. The basic usage video should be the quick start instructions.

Still thinking through it, but I'd like to try the reformat.