My "Add" button doesn't work either. I've wondered whether it has to do with this line in the ReadMe file:
I don't know enough about Ruby to know how to grant such permission, so if this is indeed the culprit, it would be wonderful if someone could write instructions for this step for the Ruby-illiterate.
|4a. If you are on OS X >= 10.5, give Ruby permission to respond to incoming network traffic.|