Bug 1019672 Add steps: pip, setup.py and running unit tests.

@bitgeeky r? If everything looks ok to you, we can run it by Bob.
This section does not specifically call out the need to set both `HMAC_KEYS` and `SECRET_KEY`, and it's not entirely obvious from the file that you need to do that. If you don't, however, the rest of the instructions won't work, so I think it's worth calling those out here.