Add note explaining MONGO_BIND_IP OPS-2205

playbooks/roles/mongo_3_2/defaults/main.yml

@@ -39,7 +39,13 @@ MONGO_USERS:
     database: edxapp
     roles: readWrite
 
+# This default setting is approriate for a single machine installation
+# This will need to be overridden for setups where mongo is on its own server
+# and/or you are configuring mongo replication. If the override value is
+# 0.0.0.0 mongo will listen on all IPs. The value may also be set to a
+# specific IP.
 MONGO_BIND_IP: 127.0.0.1
+
 MONGO_REPL_SET: "rs0"
 MONGO_AUTH: true