Add guide for Google Cloud Engine.

[fcuny]

This is a first attempt to document the GCE modules.

Please bear in mind that I'm not a native speaker, but I'm more than happy to improve and update this PR.

(cc @erjohnso).

Thanks.

[mpdehaan]

Very nice! This comes at a very good time actually.

I hope to get this reviewed and up this week. Thanks very much!

[erjohnso]

Google marketing folks would prefer "Google Cloud Platform Guide" if you don't mind.

[erjohnso]

Great work @franckcuny! I had a few small suggestions but otherwise, this is really great to see and thank you!

[fcuny]

I've fixed all the suggestions. This should be good to go.

[mpdehaan]

Working on merging this in now!

[mpdehaan]

All merged in, I also updated this a bit to show the usage of tags rather than hostnames to manage cloud "more like cloud", and also updated somethings stylistically to make them not have to rely on "local_action" which makes formatting a little better.

Some of these changes have not had the full benefit of testing and review, so if you would like to help look these over I can easily push updates.

That all being said, this is now integrated into the docs and I'll be kicking off a docs build/push ...
NOW.

Other upgrades are of course also welcome -- like maybe crosslinking to the GCE modules pages?

Thanks very much for this, great to see the guide sections being built out further.

Much appreciated!