Documentation update for issue #467

Added information that refrences setup.py's unit testing functionality.
I have updated the examples that refer to unittest. Should the be removed? Will a developer still find the unittest commands to be useful when they are trying to run a specific test?
@mtomwing should the Gotchas/QA section be removed too? It could be written again later if running unit tests starts having gotchas.
In addition, should I open an issue to update the testing page to reflect testing with the pytest way?