[README] Change license phrasing.

Note that the non-code content is released under public domain, not the
MIT license with everything else.  Why?  Because MIT isn't designed for
artworks.  I should probably clarify, but I'll do that later.
Merge branch 'master' of github.com:NuckChorris/assault
[README] Fixing image URLs now that errything's under img/
Not so pretty initial commit of AwesomeWM port