Update to readme.md

Some proposed initial changes to the readme to give a very quick intro and links out to the docs. All new content pulled in from other locations in the repo; will be cleaning up all pages over the next little while.
Fair comment :) I'm trying to clean up the information so that it's more clear. We have a lot of good info that's spread out and hard to find - the docs/overview.md, for example, has good info that can be merged into some of the other overview style pages (or built out to be *the* overview of the project).

Initially I'd like to concentrate on two things:

1 - consolidating pages
2 - increasing discoverability and giving some indication of the order in which to read the docs
(okay that's three things :) )

Each folder should have a readme that describes its contents. The list of docs in the docs/readme.md is great; we also need to list out/describe the pages that are in that folder.