Document the .eslintrc file

Most people are much more familiar with jsHint than eslint, myself included. When I wanted to see what was enforced for this project and first saw the wall of config that is the `.eslintrc` file I felt pretty out of my depth. 

In an effort to make this a little more approachable I've decided to use a little regex magic to document the `.eslintrc` file in the same way that [jsHint](https://github.com/jshint/jshint/blob/master/examples/.jshintrc) does. You has already done most of the hard work by copying the master rules list so this PR just adds a little documentation straight off of the [rules page](http://eslint.org/docs/rules/). Your rules should still be in place and should still warn at the appropriate levels.