Minor Feedback Updates to Interview Problem

This is just some minor updates to the interview project that I thought would have been nice after I had taken it:

1) Updated the readme to reflect setup instructions so no one forgets to run db:migrate and db:seed.  I contemplated writing instructions on what to for the assignment, but I did not know whether or not you wanted to expose the problem before the interview so I refrained from doing so.

2) Moved the underwritings.csv to an alternate location (/public in this case).  The csv could been placed in many places, but an assets directory inside of the spec isn't one of them since it makes no technical sense.  I think /public is a good place for it since it flows with the story of the assignment that the csv was uploaded by a user, but feel free to place it in a different location if you wish.

3) Added annotations to the three models.  I found myself frequently looking at the migrations to figure out the names and types of the data stored on the models till we realized that I had not run db:seed, in which case I moved to my sqlite viewer.  Regardless, reading migration files is kind of a pain when trying to grok a table structor and names you've never seen before, and I would have found it a lot easier to sort out the mappings of the CSV to the models with some annotations of the db structor on the modesl.