updated supported platforms (#801)

Author: cahoonpwork

hugo/content/gettingstarted/prereq/_index.md

@@ -9,7 +9,9 @@ weight: 20
 
 The following is required prior to installing PostgreSQL Operator:
 
-* Kubernetes v1.11+ or OpenShift v3.09+
+* Kubernetes v1.13+
+* Red Hat OpenShift v3.11+
+* VMWare Enterprise PKS 1.3+
 * `kubectl` or `oc` configured to communicate with Kubernetes