Add a small section to explain how to use "OS::stack_id" in outputs
Add a small section to explain how to use "OS::stack_id" in outputs

Change-Id: If691b24f3aa73edb46ec40e96992360c4c667c81

AlekhyaMallina-Vedams/openstack-manuals,openstack/openstack-manuals,gongysh2004/openstack-manual,potsmaster/openstack-manuals,AlekhyaMallina-Vedams/openstack-manuals,openstack/openstack-manuals,openstack/openstack-manuals,saeki-masaki/openstack-manuals,openstack/openstack-manuals,gongysh2004/openstack-manual,saeki-masaki/openstack-manuals,AlekhyaMallina-Vedams/openstack-manuals,Akasurde/openstack-manuals,kairoaraujo/openstack-manuals,Akasurde/openstack-manuals,potsmaster/openstack-manuals,kairoaraujo/openstack-manuals