Docs

A first version of some documentation (see issue #18). For now, I only:

* Created a walkthrough
* Created a simple README
* Moved specs files in doc files (mostly just moved content)
* Removed some spec files that _looked like_ out of date (please make sure that's ok)

If merged, new PR will include documentation updates.

Let me know what you think :) (After that, I think it'll be enough documentation for now for me :P)
Is 'on' needed here?