[Doc moveit_config] Add a note about joint_limits.yaml (UniversalRobots#1764)

Author: urfeex

ur_moveit_config/doc/index.rst

@@ -49,3 +49,11 @@ robot as explained `here <https://moveit.picknik.ai/main/doc/tutorials/quickstar
       :start-at: trajectory_execution:
       :end-at: execution_duration_monitoring
       :caption: moveit_controllers.yaml
+
+.. note::
+   The MoveIt configuration does contain a ``joint_limits.yaml`` file as it is autogenerated by the
+   MoveIt Setup Assistant. The joint limits overwrite / augment the ones from the description. This
+   means that any limits defined here that are also defined in the URDF will be used from the
+   moveit_config ``joint_limits.yaml`` in the context of MoveIt motion planning.
+   One way to interpret this is that the URDF describes the hardware's limits, while the
+   moveit_config provides limits on an application / planning level.