DOCSP-22342 BACKPORT (#1034)

Author: Dave

source/reference/operator/aggregation/setWindowFields.txt

@@ -406,7 +406,7 @@ in :pipeline:`$setWindowFields` to output the cumulative cake sales
 
 In the example:
 
-- ``partitionBy: "$state"`` :ref:`partitions
+- ``partitionBy: { $year: "$orderDate" }`` :ref:`partitions
   <setWindowFields-partitionBy>` the documents in the collection by
   :expression:`$year` in ``orderDate``. There are are partitions for
   ``2019``, ``2020``, and ``2021``.