Add migration notes for jazzy (#1045)

ur_robot_driver/doc/migration/jazzy.rst

@@ -8,3 +8,46 @@ Doing real-time control with a robot requires the control pc to conform to certa
 constraints. For this ``keep_alive_count`` was used to estimate the tolerance that was given to the
 ROS controller in terms of multiples of 20 ms. Now the timeout is directly configured using the
 ``robot_receive_timeout`` parameter of the hardware interface.
+
+
+ros2_control xacro tag moved to driver package
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+The description package no longer adds the ``ros2_control`` tag to the robot's URDF. This is done
+in the driver now. Therefore, there is a ``urdf`` folder containing the macro for generating a
+``ros2_control`` tag and a ready-to-use xacro file for a UR robot with a ``ros2_control`` tag.
+
+If you want to create your own controlled robot, you should mimic that structure, as done e.g. in
+the `custom_workcell_tutorial`_.
+
+.. _custom_workcell_tutorial: https://github.com/UniversalRobots/Universal_Robots_ROS2_Tutorials/blob/main/my_robot_cell/my_robot_cell_control/urdf/my_robot_cell_controlled.urdf.xacro
+
+robot_description is now distributed by the robot_state_publisher
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+The ``robot_description`` isn't propagated to all interested parties as a parameter. Instead, only
+the ``robot_state_publisher`` is provided with the parameter, republishing it on the
+``robot_description`` topic.
+
+Therefore, there is a new launchfile ``ur_rsp.launch.py`` which takes care about loading the
+description and starting the ``robot_state_publisher``. If you create a description that needs
+other parameters than the packaged one, you can write your own ``rsp`` launch file and pass that as
+``description_launchfile`` argument to ``ur_control.launch.py``.
+
+Enforce absolute paths in launchfiles
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+All launchfiles now expect an absolute path for files that should be used to alter the launch
+process (e.g. description file, controllers file). Before it was expecting e.g. a
+``description_package`` and a ``description_file`` argument with a relative path to the package.
+
+The default files have not been changed, so unless you specified your custom package / file
+combinations, you will need to update that to an absolute path.
+
+Absolute paths can still be generated dynamically using a package + relative path structure inside
+other launchfiles or by using ``ros2 pkg prefix`` on the command line. For example, you can do
+
+.. code-block:: console
+
+   $ ros2 launch ur_robot_driver ur_control.launch.py ur_type:=ur20 robot_ip:=192.168.56.101 \
+     kinematics_params_file:=$(ros2 pkg prefix my_robot_cell_control)/share/my_robot_cell_control/config/my_robot_calibration.yaml