Update the README, import Compass and add an index.php

This pull request adds the following:

1. Updates the readme to explain how `grunt watch` works for people like myself who were used to using Compass.app to watch folders.
2. Import Compass seeing we use it in every plugin now.
3. Stop potential directory browsing on bad hosts by having a 'silence is golden' index.php.

I think I've earnt a :star: now :stuck_out_tongue: