Add more developer documentation.

This is 'in process' stuff I have been writing up, so please don't merge it yet, even if you think these are the best directions you have ever read (yeah, right!).  I just want to get some feedback that I could incorporate tomorrow (otherwise I am gone for over a week, so this will sit).  Does it make sense to have all this stuff in the CONTRIBUTING file?  Perhaps a GETTING_STARTED or something else instead?  I suppose it could even go on the wiki, but I would rather have it right there for developers after the repo is cloned. I plan to add more info about models and perhaps a little on migrations, but the main thing I want in here is something on tests, which I currently have no idea how to write up.  This is the main part I want to look at tomorrow.  Any feedback/improvement suggestions welcome.

-j