DOCSP-18788 postprocessor text fix (#175)

DOCSP-18788: postprocessors grammar fix

Author: Chris Cho

source/sink-connector/fundamentals/post-processors.txt

@@ -49,9 +49,10 @@ result in a MongoDB collection.
 
 Post processors perform data modification tasks such as generating
 the document ``_id`` field, projecting message key or value fields, and
-renaming fields. You can implement your own post processor by extending the
+renaming fields. You can use the prebuilt post processors included in the
+connector, or you can implement your own by extending the
 `PostProcessor <https://github.com/mongodb/mongo-kafka/blob/master/src/main/java/com/mongodb/kafka/connect/sink/processor/PostProcessor.java>`_
-class or you can use one of the following prebuilt ones.
+class.
 
 .. _sink-post-processors-specify: