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!
Sorry I'm late to this party. I agree with you both. `contrib` is kind of weird (I read a long rant against the very idea recently), but I think this is ok to add as is. We obviously want to support GCE to whatever extent possible but it's not quite at the same level as EC2 yet. I don't think this will be particularly confusing given Rackspace in limbo, etc.