Add some notes about controls

Hi there,

I saw [your post on Reddit](http://www.reddit.com/r/gamedev/comments/176w63/my_3rd_person_spaceship_controls_in_unity_ill/). I love this repository!!! 

I found it hard to figure out the controls from the website, so I humbly submit a pull request for your consideration (you can see what it will look like at http://leereilly.net/Chromeshadows/).

Cheers,
  Lee :beers: