The docs were in need of some restructuring wrt prerequisites. They
were mingled with general k8s and Ceph requirements. For clarity,
we need to separate the ceph prereqs from general k8s requirements.

There is now only a single prereqs page. All other topics should be
found under other sections, such as specific to Ceph. Having subtopics
under the general prereqs caused users to frequently not even notice
the main prereqs topic.
Signed-off-by: Travis Nielsen <tnielsen@redhat.com>