docs: use sentence case for headings

This adheres to the IBM Style Guide for capitalisation. I'm not updating
the Installation Guide in this patch as I have other plans for it.

Change-Id: I5652dcaedc287135bcb2d8f16c0bfc423a7d8d5b
docs: fix a couple of links missed in the sphinx conversion

Change-Id: I20a67269e9d4db73283fa8510c6c0e698cf104d8
docs: merge Installation Guide into Admin and User Guides

Change-Id: Id9168dcca7c83337617defca0898ac2540b3c094
Merge changes Id9168dcc,I20a67269,I5652dcae into release-0.11

* changes:
  docs: merge Installation Guide into Admin and User Guides
  docs: fix a couple of links missed in the sphinx conversion
  docs: use sentence case for headings