Added usage with NSURLSession

This being my first time using VOKMockUrlProtocol, I had to dig around with Parche to find how VOKMockUrlProtocol is actually used by the configuration. Hopefully these docs clear it up.
Merge pull request #15 from jacobvanorder/patch-1

Added usage with NSURLSession
Merge pull request #16 from vokal-isaac/master

Oh, Travis.