Add Known Issue to Dashing about ros2/rclcpp#781 (#303)

source/Releases/Release-Dashing-Diademata.rst

@@ -771,7 +771,7 @@ Known Issues
   Currently available workarounds are noted in an `issue comment <https://github.com/ros2/rclcpp/issues/715#issuecomment-497392626>`_
 * `[ros2/rclpy#360] <https://github.com/ros2/rclpy/issues/360>`_ rclpy nodes ignore ``ctrl-c`` when using OpenSplice on Windows.
 * `[ros2/rosidl_typesupport_opensplice#30] <https://github.com/ros2/rosidl_typesupport_opensplice/issues/30>`_ There is a bug preventing nesting a message inside of a service or action definition with the same name when using OpenSplice.
-
+* `[ros2/rclcpp#781] <https://github.com/ros2/rclcpp/pull/781>`_ Calling ``get_parameter``/``list_parameter`` from within ``on_set_parameter_callback`` causes a deadlock on Dashing.  This is fixed for Eloquent, but is an ABI break so has not been backported to Dashing.
 
 Timeline before the release
 ---------------------------