Mongo configServer should have at least 3 repliacs

Signed-off-by: Arnob kumar saha <[email protected]>

docs/addons/mongodb/sharding/index.md

@@ -90,6 +90,9 @@ $ kubectl apply -f https://github.com/stashed/docs/raw/{{< param "info.version"
 mongodb.kubedb.com/sample-mgo-sh created
 ```
 
+According to MongoDB [docs](https://www.mongodb.com/docs/manual/core/replica-set-members/#replica-set-members), we should always have at least 3 replicas in the replicaSet.
+As one secondary gets locked while running mongodump utility, This is a must, in case of configServer while taking backup. There can be various issues like sharding commands get stucked, primary-secondary syncing issue etc. if you don't specify >= 3  replicas in `.spec.shardTopology.configServer.replicas` field. 
+
 KubeDB will deploy a MongoDB database according to the above specification. It will also create the necessary secrets and services to access the database.
 
 Let's check if the database is ready to use,