Update readme-vars.yml

Fix `readme.md` the correct way.

Author: rdehuyss

readme-vars.yml

@@ -79,7 +79,8 @@ app_setup_block: |
     roles: [
       { db: "${MONGO_DBNAME}", role: "dbOwner" },
       { db: "${MONGO_DBNAME}_stat", role: "dbOwner" },
-      { db: "${MONGO_DBNAME}_audit", role: "dbOwner" }
+      { db: "${MONGO_DBNAME}_audit", role: "dbOwner" },
+      { db: "admin", role: "clusterMonitor" }
     ]
   })
   EOF