Additional setup helpers for the app + fix for missing facebook.yml

1. environmental variable can be added to a .rvmrc file (if you are using rvm
this needs to be ignored by git, since email & password is stored in plain text

2. I tried a migration & got error, saying config/facebook.yml is missing.
thus I created the file, ignore it in git (same reason as above)

3. update docs to reflect these changes