Fix/position

The octokit api expects position, not line number, which is what you are giving it, however this keeps it all named the same.

I also updated the readme with a step I needed to get it running locally.

This all passes except [this test](https://github.com/thoughtbot/hound/issues/311) which failed on a clean slate.
Is `RAILS_ENV=test` needed? Doesn't `db:setup` prepare both dev and test databases?