DOCSP-34843 config Database Clarification (#6411) (#6523)

* DOCSP-34843 Adds note for config on mongos

* Moves the note under intro

* Fixes build issue

* Adds facet

* minor edits

* minor edits

* Fixes per Lauren

Author: kennethdyer

source/reference/config-database.txt

@@ -20,6 +20,26 @@ The collections in the ``config`` database support:
   <sessions>` for standalones, replica sets, and sharded clusters and
   retryable writes for replica sets and sharded clusters.
 
+.. note::
+   
+   Sharded clusters may show different collections in the
+   ``config`` database, depending on whether you connect to
+   :program:`mongos` or :program:`mongod`:
+
+   - On ``mongos``, the ``config`` database shows collections
+     located on the config servers, such as
+     :data:`~config.collections` or :data:`~config.chunks`.
+
+   - On ``mongod``, the ``config`` database shows
+     collections specific to the given shard, such as
+     :data:`~config.migrationCoordinators` or
+     :data:`~config.rangeDeletions`.
+
+   When a config server and a shard are hosted on the same node,
+   :program:`mongos` may have access to some shard-local
+   collections in the ``config`` database.
+
+
 Restrictions
 ------------