Read Me Cleanup

This PR cleans up the readme a bit, moving some API specific items to the API docs.

The assumption I am working under is that once helpful is running on a machine, all other setup happens in the app itself (i.e. instructions to curl a new message/email a new message).

There is no specific WIP for this, but there is a bit of related discussion here: https://assemblymade.com/helpful/wips/168