Update release notes

doc/release_notes.rst

@@ -74,6 +74,7 @@ controller_manager
 * The support for the ``description`` parameter for loading the URDF was removed (`#1358 <https://github.com/ros-controls/ros2_control/pull/1358>`_).
 * The ``--controller-type`` or ``-t`` spawner arg is removed. Now the controller type is defined in the controller configuration file with ``type`` field (`#1639 <https://github.com/ros-controls/ros2_control/pull/1639>`_).
 * The ``--namespace`` or ``-n`` spawner arg is deprecated. Now the spawner namespace can be defined using the ROS 2 standard way (`#1640 <https://github.com/ros-controls/ros2_control/pull/1640>`_).
+* ``--controller-manager-switch-timeout`` was added as parameter to the helper scripts ``spawner.py`` and ``unspawner.py`` (`#1790 <https://github.com/ros-controls/ros2_control/pull/1790>`_).
 
 hardware_interface
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