Document rizzo layouts

After our discussion the other day I wanted to document how the main page layouts work and why we split the UI into rows, as well as where the content fits in.

![image](https://cloud.githubusercontent.com/assets/814861/3110925/11296052-e6ab-11e3-9591-78dd990728db.png)

![image](https://cloud.githubusercontent.com/assets/814861/3110921/065de10c-e6ab-11e3-9c57-3d00617fedc5.png)