Sublime Text removed some trailing whitespace for me.
Add uber-important note from the Apple docs warning about function calls & NSAssert

  * https://developer.apple.com/library/mac/documentation/Cocoa/Reference/Foundation/Miscellaneous/Foundation_Functions/Reference/reference.html#//apple_ref/c/macro/NSAssert
Merge pull request #2 from medington/master

Remove trailing whitespace and add important note to NSAssert section