DOCSP-11073: Add multiple collection example for Source Connector (#36)

add PR template

Author: Chris Cho

source/kafka-source.txt

@@ -143,6 +143,8 @@ an example source connector configuration file, see
 
        .. seealso:: :ref:`Custom pipeline example <custom-pipeline-example>`.
 
+       .. seealso:: :ref:`Multiple source example <multi-source-example>`.
+
        | **Default**: []
        | **Accepted Values**: A valid JSON array
 
@@ -261,6 +263,24 @@ to filter or modify the change events output. In this example, we set the
    ``_id`` field which MongoDB uses as the :manual:`resume token
    </changeStreams/#change-stream-resume-token/>`.
 
+.. _multi-source-example:
+
+Multiple Source Example
+-----------------------
+
+You can configure the source connector to listen for events from multiple
+collections by using the ``pipeline`` configuration with a custom 
+:manual:`aggregation pipeline </reference/operator/aggregation-pipeline/>`
+to match your collection names.
+
+The following sample configuration shows how you can set your source
+connector to listen to the ``collection1`` and ``collection2``
+collections by matching with a regular expression on the collection names:
+
+.. code-block:: properties
+
+   pipeline=[{"$match": {"ns.coll": {"$regex": /^(collection1|collection2)$/}}}]
+
 .. _topic-naming-example:
 
 Topic Naming Example