Adding some useful info to readme.

This was something that tripped me up, so I figured other people might
find it useful, too.
Added game scene.

Stubbed out the game scene. It's startup command creates a 4x4 grid of
disk prefabs.
Creating wrappers for Resources and GameObject.

Updated GameStartupCommand to use wrappers instead of Unity's static
classes.
Merge pull request #1 from wlindley/master

Adding some useful info to readme.