Add policy description for 'limits'
Add policy description for 'limits'

This commit adds policy doc for 'limits' policies.

Partial implement blueprint policy-docs

Change-Id: Iba3ac6804f105e3ec9cc0bf8187fb35710c929f6

phenoxim/nova,vmturbo/nova,gooddata/openstack-nova,mikalstill/nova,vmturbo/nova,klmitch/nova,klmitch/nova,rahulunair/nova,jianghuaw/nova,gooddata/openstack-nova,mikalstill/nova,Juniper/nova,openstack/nova,gooddata/openstack-nova,mikalstill/nova,jianghuaw/nova,klmitch/nova,vmturbo/nova,Juniper/nova,Juniper/nova,rahulunair/nova,jianghuaw/nova,rahulunair/nova,openstack/nova,mahak/nova,openstack/nova,gooddata/openstack-nova,phenoxim/nova,vmturbo/nova,jianghuaw/nova,Juniper/nova,klmitch/nova,mahak/nova,mahak/nova