Added onos.app.url for openflow provider

 - temporary choice, so we have something interesting for ONS demo.
 - it would be better if openflow provider had a wiki page.

Change-Id: I8c9216782f9b8c5de0a07bb7985b988b86320203

@@ -36,6 +36,9 @@
             org.onosproject.hostprovider,
             org.onosproject.lldpprovider
         </onos.app.requires>
+        <onos.app.url>
+            https://wiki.onosproject.org/display/ONOS/Application+Subsystem
+        </onos.app.url>
     </properties>
 
     <description>OpenFlow southbound meta application</description>