docsite, cloudstack: add limited VPC support

Also see https://github.com/ansible/ansible-modules-extras/issues/1811

docsite/rst/guide_cloudstack.rst

@@ -23,6 +23,10 @@ You'll need this Python module installed on the execution host, usually your wor
 
 .. note:: cs also includes a command line interface for ad-hoc interaction with the CloudStack API e.g. ``$ cs listVirtualMachines state=Running``.
 
+Limitations and Known Issues
+````````````````````````````
+VPC support is not yet fully implemented and tested. The community is working on the VPC integration.
+
 Credentials File
 ````````````````
 You can pass credentials and the endpoint of your cloud as module arguments, however in most cases it is a far less work to store your credentials in the cloudstack.ini file.