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.
I think it's slightly misleading that under `Development` heading we use the `test` environment. The more appropriate way to setup the `test` db is to run `rake db:test:prepare` afterwards. I've documented this in #314.