Add documentation around ignoring js files

https://trello.com/c/N8xHlYlK/
Ah, I see what your saying.

How about replacing the entire 2 paragraphs with:

"Hound will automatically ignore any files that are specified in a `.jshintignore` file in the root of your project. If you would like to instruct Hound to use a different ignore configuration file, you can do so by adding the following to `.hound.yml` in the root of your project."