Update GCE install doc for newer instructions and more clarity

-@Sirclicksalot.

Created more detailed guide for installing docker on a Google Compute Engine instance using `gcloud` and `gcutil`. Cleaned up formatting to allow for nested code blocks in a numbered list.

docs:/ amendments to google.md viad pr#5465

-@ostezer.

This commit builds on the initial google.md improvements proposed
in pr#5465.

It fixes the general structural and marking issues.

Docker-DCO-1.1-Signed-off-by: O.S. Tezer <ostezer@gmail.com> (github: @ostezer)