Fixes the harmful changes made to readme

Last night a lot of stuff that makes no sense was added to the readme

 - removes instructions to clone the repo, this is obvious to any open source contributor
 - removes instructions to install rvm and directs the user to the RVM docs
 - removes rails installation from dependency. wtf would you need rails for?
 - adds proper instructions for installing node from a package manager
 - proper instructions for initializing n
 - run npm install instead of installing grunt-contrib-compass 

references issue #6