Add Contributor's Guide

I saw this awesome link in the latest Ruby Weekly:

http://silverhammermba.github.io/emberb/

I thought that this project should advertise it somehow. But how? I thought that stuff like that goes to some kind of contributor's guide. This project didn't have a contributor's guide. So I decided to create it and insert this link there :)

It looks incomplete. I really have no idea what else to add. I think my caffeine level dropped. Suggestions?