Update release_notes

Author: saikishor

doc/release_notes.rst

@@ -9,6 +9,8 @@ controller_manager
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 * The default strictness of the ``switch_controllers`` can now we be chosen using ROS 2 parameters. The default behaviour is still left to ``BEST_EFFORT`` (`#2168 <https://github.com/ros-controls/ros2_control/pull/2168>`_).
 * Parameter ``shutdown_on_initial_state_failure`` was added to avoid shutting down on hardware initial state failure  (`#2230 <https://github.com/ros-controls/ros2_control/pull/2230>`_).
+* The controller manager now supports switching (activating and deactivating) controllers in both realtime and non-realtime modes. This is controlled by the parameter ``activate_asap`` of the ``switch_controllers`` service (`#2452 <https://github.com/ros-controls/ros2_control/pull/2453>`_).
+* The spawner now supports two new arguments ``--switch-asap`` and ``--no-switch-asap`` to control the behaviour of the spawner when switching controllers to be in realtime loop (or) non-realtime loop (`#2452 <https://github.com/ros-controls/ros2_control/pull/2453>`_).
 
 hardware_interface
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