Update Foxy Release Notes after ros2/rviz#519 (#568)

* Update Foxy Release Notes after ros2/rviz#519

Signed-off-by: Michel Hidalgo <michel@ekumenlabs.com>

* RST wants double quotes, not single.

Co-authored-by: Katherine Scott <katherineAScott@gmail.com>

source/Releases/Release-Foxy-Fitzroy.rst

@@ -110,6 +110,16 @@ The method ``set_parameters_calblack`` has been deprecated.
 
 Related pull requests: https://github.com/ros2/rclpy/pull/457, https://github.com/ros2/rclpy/pull/504
 
+rviz
+^^^^
+
+Tools timestamp messages using ROS time
+"""""""""""""""""""""""""""""""""""""""
+
+'2D Pose Estimate', '2D Nav Goal', and 'Publish Point' tools now timestamp their messages using ROS time instead of system time, in order for the ``use_sim_time`` parameter to have an effect on them.
+
+Related pull request: https://github.com/ros2/rviz/pull/519
+
 Timeline before the release
 ---------------------------