autohelp: add oslo.service to the list of extensions
autohelp: add oslo.service to the list of extensions

Change-Id: Id523dd72c5987f86d22bd5905ed1511b58ae25cf
Closes-Bug: #1487171

savinash47/openstack-doc-tools,openstack/openstack-doc-tools,savinash47/openstack-doc-tools,savinash47/openstack-doc-tools,openstack/openstack-doc-tools