update release notes

doc/release_notes.rst

@@ -83,6 +83,7 @@ controller_manager
 * The ``ros2_control_node`` node has a new ``lock_memory`` parameter to lock memory at startup to physical RAM in order to avoid page faults (`#1822 <https://github.com/ros-controls/ros2_control/pull/1822>`_).
 * The ``ros2_control_node`` node has a new ``cpu_affinity`` parameter to bind the process to a specific CPU core. By default, this is not enabled. (`#1852 <https://github.com/ros-controls/ros2_control/pull/1852>`_).
 * The ``--service-call-timeout`` was added as parameter to the helper scripts ``spawner.py``. Useful when the CPU load is high at startup and the service call does not return immediately (`#1808 <https://github.com/ros-controls/ros2_control/pull/1808>`_).
+* The ``cpu_affinity`` parameter can now accept of types ``int`` or ``int_array`` to bind the process to a specific CPU core or multiple CPU cores. (`#1915 <https://github.com/ros-controls/ros2_control/pull/1915>`_).
 
 hardware_interface
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