Add information about which driver features dont work with mock hardware (#1227)

Mock hardware doesn't support every feature of the driver at the moment. This should be made clear in the documentation.

Author: URJala

ur_robot_driver/README.md

@@ -33,7 +33,7 @@ request.
 **Custom script snippets** can be sent to the robot on a topic basis. By default, they will
 interrupt other programs (such as the one controlling the robot). For a certain subset of functions,
 it is however possible to send them as secondary programs. See [UR
-documentation](https://www.universal-robots.com/how-tos-and-faqs/how-to/ur-how-tos/secondary-program-17257/)
+documentation](https://www.universal-robots.com/articles/ur/programming/secondary-program/)
 on details.
 <br/>
 **Note to e-Series users:**

ur_robot_driver/doc/usage/simulation.rst

@@ -43,3 +43,11 @@ environment for testing of "piping" of hardware and controllers, as well as test
 descriptions. For more details see `ros2_control documentation
 <https://control.ros.org/rolling/doc/ros2_control/hardware_interface/doc/mock_components_userdoc.html>`_
 for more details.
+
+.. note::
+   Some driver functionalities currently don't work with mock hardware:
+
+   * The TCP pose broadcaster does not work.
+   * The passthrough trajectory controller does not function when calling the follow joint trajectory action.
+   * The force mode controller also does not respond when trying to start force mode.
+   * The GPIO controller cannot verify that it has changed the state of an I/O pin, so it will report a failure when trying to set an I/O pin.