The "Convert a Replica Set to a Sharded Cluster" documentation is not explicitly saying when a user is expected to stop pointing to the replica set and start pointing to the router.

Purpose of this ticket is to explicitly write it down at the end of the "Add initial replica set as a shard" section.

We should state something like: "Starting from this moment, clients must ALWAYS point to the router and never target directly the old replica set (aka the newly added shard)".