Move screenshots from README to a "advertising" web site

[NicMcPhee]

Projects usually reserve their Github repo README for "tech" info like building, installation, and some basic documentation (see, e.g., Middleman). They then put "advertising" material on a more "general purpose" web site (e.g., Middleman's home page). It's pretty easy to create this sort of "advertising" home page via Github Pages, which integrates nicely with Github, etc., so moving all the screen shots and advertising info over there wouldn't be too hard.