Simplified quickstart instructions

@pbrisbin It was not my intention to take a shot at the script by any means. Thanks for the clarification.

> Anything bin/setup-like would be good enough for me.

Agreed. I'm in favor of what's being suggested and I am not trying to push a Makefile onto Yesod either. 

I did mock up a quick Makefile in case it is ever considered, though :).

https://gist.github.com/creichert/1dc8ea3eb819c27d693b