Workflow documentation is now in infra-manual

Replace URLs for workflow documentation to appropriate parts of the
OpenStack Project Infrastructure Manual.

Change-Id: I48d86e8474ee83f538b21790eb4de46a5b785547

CONTRIBUTING.rst

@@ -1,13 +1,13 @@
 If you would like to contribute to the development of OpenStack,
 you must follow the steps documented at:
 
-   https://wiki.openstack.org/wiki/How_To_Contribute#If_you.27re_a_developer
+   http://docs.openstack.org/infra/manual/developers.html#development-workflow
 
 Once those steps have been completed, changes to OpenStack
 should be submitted for review via the Gerrit tool, following
 the workflow documented at:
 
-   https://wiki.openstack.org/GerritWorkflow
+   http://docs.openstack.org/infra/manual/developers.html#development-workflow
 
 Pull requests submitted through GitHub will be ignored.