Add Kubernetes section to User Guide
Add Kubernetes section to User Guide

Kubernetes section

This section covers creating and managing Kubernetes bay.
Details and links include networking, storage, image,
TLS, external load balancer.

Partially implements: blueprint user-guide
Change-Id: I7e5a9e92d4f9746ca37074a7eebfe8474591d542

openstack/magnum,ArchiFleKs/magnum,ArchiFleKs/magnum,openstack/magnum