Add oslo.policy to openstack project list

Since oslo.policy is on the graduation track, the repo has been
created and has some docs that are live, lets's include it in
this page.

Change-Id: I0a914d21e2226a8f2914b5b820b19345e168d26c

www/developer/openstack-projects.html

@@ -173,6 +173,12 @@
     </a>
     - A collection of WSGI middleware for web service development.
    </dd>
+   <dd>
+    <a href="http://docs.openstack.org/developer/oslo.policy/">
+     oslo.policy
+    </a>
+    - Provides common policy enforcement.
+   </dd>
    <dd>
     <a href="http://docs.openstack.org/developer/oslo.rootwrap/">
      oslo.rootwrap