Added Cheat Sheet

During the class at PyOH, one of the adult volunteers suggested we
create a cheat sheet at lunch so they children would know how to turn on
the Raspberry Pi's, log in, and start x.  I handed him my laptop and
said have at it, so he put together this very nice cheat sheet.  I
believe Katie Cunningham made some edits.
Merge pull request #3 from w3ttr3y/master

Added Cheat Sheet