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?
Try to write documentation concisely, but without losing important details.

For example, this can be reduced to

> To run all of the unit tests in `freeseer/tests/`, run the following command from the `freeseer/src/` directory: