fixup: add more information about external odometry sources

dev/source/docs/ros2-interfaces.rst

@@ -196,6 +196,12 @@ For more information on the coordinate systems used, review `ROS REP-105 <https:
    </tbody>
    </table>
 
+.. warning:: 
+   Only the dynamic transformations on ``/ap/tf`` that have parent_frame ``odom`` and child_frame ``base_link`` are fed into ``AP_VisualOdom``. 
+   Other frame configurations will be gracefully ignored, so feel free to populate this topic with other transforms if that's convenient.
+
+For more information on how to setup ArduPilot with an external odometry source, 
+see the :ref:`cartographer SLAM example<ros2-cartographer-slam>.
 
 Configuring Interfaces at Compile Time
 ======================================