Merge pull request #3050 from lorin/os-grizzly-only

Document: OpenStack inventory script needs grizzly

docsite/latest/rst/api.rst

@@ -306,7 +306,8 @@ To see the complete list of variables available for an instance, run the script
 Example: OpenStack Inventory Script
 ```````````````````````````````````
 
-Though not detailed here in as much depth as the EC2 module, there's also a OpenStack Nova external inventory source in the plugins directory.  See the inline comments in the module source for how to use it.
+Though not detailed here in as much depth as the EC2 module, there's also a OpenStack Compute external inventory source in the plugins directory. It requires the Grizzly release of OpenStack or
+later. See the inline comments in the module source for how to use it.
 
 Callback Plugins
 ----------------