Clarify etcd deployment script failure mechanism

Attempting to clarify the language surrounding the etcd node deployment script failure mechanism. I had this error when doing a new cluster deployment last night and, though it should have been, it wasn't immediately apparent to me what was causing the issue (since my default master node hostnames do not specify whether they are also acting as etcd replicas).

contrib/terraform/openstack/README.md

@@ -32,7 +32,11 @@ floating IP addresses or not.
 - Kubernetes worker nodes
 
 Note that the Ansible script will report an invalid configuration if you wind up
-with an even number of etcd instances since that is not a valid configuration.
+with an even number of etcd instances since that is not a valid configuration. This
+restriction includes standalone etcd nodes that are deployed in a cluster along with
+master nodes with etcd replicas. As an example, if you have three master nodes with 
+etcd replicas and three standalone etcd nodes, the script will fail since there are 
+now six total etcd replicas.
 
 ### GlusterFS
 The Terraform configuration supports provisioning of an optional GlusterFS