docs: update code-review guide for config options
docs: update code-review guide for config options

We recently came to the conclusion that the original idea how the
config options of Nova should be documented are too hard to maintain.
The discussion can be found on the ML starting with:
http://lists.openstack.org/pipermail/openstack-dev/2016-May/095538.html

This change reflects the outcome of the discussion.

Change-Id: I27b2cbb663f3c9a8c2503c3148280a3844f69cdd

klmitch/nova,rahulunair/nova,jianghuaw/nova,Juniper/nova,klmitch/nova,mikalstill/nova,hanlind/nova,Juniper/nova,sebrandon1/nova,hanlind/nova,vmturbo/nova,rajalokan/nova,mikalstill/nova,jianghuaw/nova,openstack/nova,rahulunair/nova,vmturbo/nova,vmturbo/nova,sebrandon1/nova,jianghuaw/nova,vmturbo/nova,openstack/nova,hanlind/nova,rajalokan/nova,klmitch/nova,Juniper/nova,openstack/nova,cloudbase/nova,mikalstill/nova,rajalokan/nova,phenoxim/nova,jianghuaw/nova,phenoxim/nova,gooddata/openstack-nova,Juniper/nova,mahak/nova,mahak/nova,mahak/nova,gooddata/openstack-nova,gooddata/openstack-nova,klmitch/nova,rajalokan/nova,gooddata/openstack-nova,rahulunair/nova,sebrandon1/nova,cloudbase/nova,cloudbase/nova