Per the spec [1]:
reference/ – any reference information associated with a project that
is not covered by one of the above categories. Library projects should
place their automatically generated class documentation here.
There are a couple of documents that focus on nova internals, but won't
necessarily be applicable to user. These are moved here.
[1] specs.openstack.org/openstack/docs-specs/specs/pike/os-manuals-migration
Change-Id: I94614c2383329e1fbed60d9c5aca3fab5170ef8f