Add minimal baremetal docs to compute admin guide.

This patch adds a minimal amount of information to the compute admin
guide for the new Baremetal driver. It primarily updates the driver and
config option lists, and includes a reference to the wiki page
for further information.

Partially addresses bug 1038344.

Change-Id: Ic1b6d424c2a6b726f5e89a0c7ddd36acf4bb94dc
Merge "Add minimal baremetal docs to compute admin guide."