docs(postgres): Add readme

ref: #18

Author: jon-nfc

manifests/postgres/README.md

@@ -0,0 +1,15 @@
+# PostgreSQL Cluster including HA Multi-cluster replication
+
+Following Components are available:
+
+- `enable-super_user_access` Enable super user account and access to cluster
+
+- `ha` Deploy replicated multi-cluster in master-slave configuration
+
+- `metrics` Enable prometheus metrics endpoint
+
+Following Overlays are available:
+
+- `Production` - Base deployment manifests
+
+- `HA` - HA Multi-Cluster deployment with replication between clusters