DOCS-14854 findOneAndUpdate sharded (#6039) (#6042)

Co-authored-by: jason-price-mongodb <jshfjghsdfgjsdjh@aolsdjfhkjsdhfkjsdf.com>

Co-authored-by: jason-price-mongodb <jshfjghsdfgjsdjh@aolsdjfhkjsdhfkjsdf.com>

Author: jason-price-mongodb

source/core/sharded-cluster-requirements.txt

@@ -39,6 +39,16 @@ Single Document Modification Operations in Sharded Collections
 
 .. include:: /includes/fact-single-modification-in-sharded-collections.rst
 
+To use :method:`~db.collection.findOneAndUpdate()` with a sharded
+collection, your query filter must include an equality condition on the
+:term:`shard key` to compare the key and value in either of these
+formats:
+
+.. code-block:: javascript
+
+   { key: value }
+   { key: { $eq: value } }
+
 .. _sharding-requirements-unique-indexes:
 
 Unique Indexes in Sharded Collections