Added setup script and updated instructions in README

I though it would be handy to compile all the setups steps into a single script. The script will run `npm install`, pull down all dependencies, and run the `grunt docs` task. I updated the readme in a few places to help explain the process.

One thing that I removed from the readme was the use of `sudo` for installing ruby gems and npm packages. I think it's generally considered a bad practice to use `sudo` to install packages because they can run arbitrary scripts as the super user. [This articles from Isaac Schlueter explains it in more detail.](http://howtonode.org/introduction-to-npm) But that's just me being nit-picky and I'm happy to add it back.