docs(gce): Instructions for running Deis in Google Compute Engine

This is some preliminary instructions for running Deis on Google Compute Engine. I adapted it slightly from https://gist.github.com/andyshinn/a78b617b2b16a2782655 to include a `create-gce-user-data` script which re-uses the existing `contrib/coreos/user-data` as a base and adds ephemeral storage formatting to store Docker data on a volume separate from root.

There is one change to existing `contrib/coreos/user-data` which may want a second pair of eyes. The permissions for the `write_files` section were being converted by PyYAML as octal (0755 would become 493). I changed this to be a string which seems to work just fine in CoreOS cloud-init.

I'm not a programmer and don't pretend to be one. Feel free to comment on ways I might improve (or reuse existing Deis Python libs) the Python script!
If it's an issue with misinterpreting the documentation, then that's on us, not you. The docs should be more clear about this :)