The explain() output on unsharded collection is under the 'shards' field. (#5493)

* add note to release notes and fix tense issue

* moved new info to 7.2 compatibilty page

Author: MongoCaleb

source/reference/method/db.collection.aggregate.txt

@@ -348,7 +348,7 @@ The operation returns a document that details the processing of the
 aggregation pipeline. For example, the document may show, among other
 details, which index, if any, the operation used. [#agg-index-filters]_
 If the ``orders`` collection is a sharded collection, the document
-would also show the division of labor between the shards and the merge
+also shows the division of labor between the shards and the merge
 operation, and for targeted queries, the targeted shards.
 
 .. note:: The intended readers of the ``explain`` output document are humans, and

source/release-notes/7.2-compatibility.txt

@@ -21,6 +21,14 @@ Compatibility Changes in MongoDB 7.2
 Backward-Incompatible Features
 ------------------------------
 
+Aggregation on Unsharded Collections
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Starting in MongoDB 7.2, the output of 
+:ref:`explain().aggregate() <example-aggregate-method-explain-option>` 
+on sharded clusters is the same for both sharded 
+and unsharded collections. The output is under the ``shards`` field.
+
 General Changes
 ---------------