Update to readme.md

Some proposed initial changes to the readme to give a very quick intro and links out to the docs. All new content pulled in from other locations in the repo; will be cleaning up all pages over the next little while.
I assume you'll add a README.md to getting-started guides. Ditto for examples.

I assume the links to other misc. docs will be put in logical places once we have a more logical organization.

Community projects/pages (CircleCI, Digital Ocean, etc.) should be moved to https://github.com/GoogleCloudPlatform/kubernetes/wiki/Kubernetes-Community. Those are the main links I don't want to lose.