Added manual mongo statefulset config docs.

doc/mongo-statefulset-config.md

@@ -0,0 +1,28 @@
+# MongoDB Replicaset Configuration
+
+Assuming that the MongoDB replicas are named `mongo-#.mongo`, where `#` is a number, and the name `mongo` after the dot (`.`) is the name of the headless service, we can initialize as:
+
+## Initialization
+Choose and initialize the primary.
+```javascript
+rs.initiate( {
+  _id: "rs0",
+  members:[ { _id: 0, host: "mongo-0.mongo:27017" } ]
+ });
+```
+Next, add the secondary members.
+```javascript
+rs.add("mongo-1.mongo:27017");
+rs.add("mongo-2.mongo:27017");
+```
+
+
+
+## Reconfiguration
+To check the status, use `rs.status()`
+To reconfigure after initialization, use:
+```javascript
+rsconf = rs.conf()
+rsconf.members = [{_id: 0, host: "mongo-0.mongo:27017"}]
+rs.reconfig(rsconf, {force: true})
+```