DOCSP-10135: add topics.regex example (#18)

Author: Chris Cho

source/kafka-sink-properties.txt

@@ -42,10 +42,20 @@ data to sink to MongoDB. For an example configuration file, see
    * - topics.regex
      - string
      - | A regular expression that matches the Kafka topics that the sink connector should watch.
-       |
+
+       .. example::
+
+          | The following regex matches topics such as 
+          | "activity.landing.clicks" and "activity.support.clicks", 
+          | but not "activity.landing.views" or "activity.clicks":
+          
+          .. code-block:: none 
+
+             topics.regex=activity\\.\\w+\\.clicks$
+
        | *Required*
        | **Note:** You can only define either ``topics`` or ``topics.regex``.
-       | **Accepted Values**: A valid regular expression
+       | **Accepted Values**: A valid regular expression match pattern using ``java.util.regex.Pattern``.
 
    * - connection.uri
      - string