Add oslo.config to developer docs landing page
Add oslo.config to developer docs landing page

Fixes bug #1182842

Change-Id: I5642f45929b6bad865071d8677b1be40ad607961

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