Missing version of ROS2 supported

[SMorettini]

I was having a problem running the tutorials. After hours of debugging I found out that the tutorial doesn't work correctly with ROS Humble, could you add the version the tutorial is designed for on the README?

In particular, I found out that in ROS Humble, ur_control.launch.py doesn't take as input description_launchfile so the UR20 is always launched and not the my_robot_cell.

[fmauch]

This is a fair point. Thanks for pointing that out.