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?
pytest is able to run the old-style tests, so you can leave the first QA alone. However anything dealing specifically with running tests with `python -m unittest` (like in the 2nd QA) should be removed.

Definitely open an issue to update the docs for pytest. This could also turn into a nice semester project for someone if they coupled it with writing/migrating tests in/to the new style.