Add info about 'supported' vs. 'unsupported' drivers as discussed at the 7 August weekly cinder meeting. Change-Id: I952a9f404db3af07f05956cd3c4565a421b04d4c
Cinder Reference Documentation (source/reference)
Introduction:
This directory is intended to hold any reference documentation for Cinder that doesn't fit into 'install', 'contributor', 'configuration', 'cli', 'admin', or 'user' categories.
The full spec for organization of documentation may be seen in the OS Manuals Migration Spec <https://specs.openstack.org/openstack/docs-specs/specs/pike/os-manuals-migration.html>.