Couple of dependencies needed to be pre-installed to use 18F init

[lauraGgit]

In order to run git init you also need to run gem install about_yml pip install poirot

[stvnrlly]

What problem did you run into? The script should alert you if you don't have these installed, but currently doesn't install them for you. See https://github.com/18F/18f-cli/blob/develop/bin/init#L12-L29