Merge pull request #93 from mcmorisi/DOCSP-45076-count-match-2

DOCSP-45076: Document that count supports different filters from countDocuments

Author: mcmorisi

source/reference/aggregation.txt

@@ -98,6 +98,14 @@ find the total number of documents which have the exact array
 
   count = coll.count({ 'categories' => [ 'Chinese', 'Seafood' ] })
 
+.. note::
+
+   The ``count`` method is not the same as the ``countDocuments``
+   method and may not support the same filters. ``countDocuments`` uses the
+   ``$match`` stage of the aggregation pipeline to filter documents. To learn more
+   about limitations of the ``$match`` stage, see :manual:`$match Restrictions </reference/operator/aggregation/match/#restrictions>`
+   in the MongoDB Server manual.
+
 Distinct
 ~~~~~~~~