Tweaked the README to be a bit more friendly and detailed

I thought the README could use some love, so I added some details about licensing and also detailed out procedures for downloading and building the project.

In addition I added a bit to the "What do you get" paragraph and tried to tighten it all up some.
@robconery the CI doesn't require an account - there's a guest login. And using @halter73 's link doesn't even prompt to login at all - it takes you straight to the guest access mode. Having a public CI is important for contributors to see what's going on, or if one of their contributions failed on the CI (but not locally).