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.
I've been using a Mac for 8 years now full time - never used Mono outside of simple curiosity. I would not have know this. I don't think I'm alone, and I certainly don't see a problem being too clear.