docs: Improve documentation on writing custom scheduler filters
docs: Improve documentation on writing custom scheduler filters

Operators can deploy their own scheduler filters. We currently provide
some minimal instructions for how to do this but it omits things like
the need to package these filters so they can be picked up correctly.

Change-Id: I725801c9c049455a0196e4664d767b81a8d4edf2
Signed-off-by: Stephen Finucane <492121341a95b3c3aab646bed44634f739dd019b@redhat.com>

klmitch/nova,rahulunair/nova,mahak/nova,mahak/nova,openstack/nova,openstack/nova,openstack/nova,rahulunair/nova,klmitch/nova,klmitch/nova,klmitch/nova,mahak/nova,rahulunair/nova