Keyop: Document how to run in a terminal

[clalancette]

Based on the comments here and here, we should document exactly how to run the keyop using ros2 run. This is necessary since we can't have launchfiles for it (launch does not pass stdin through to processes). As reference, the documentation would say something like:

Eloquent:

ros2 run kobuki_keyop kobuki_keyop_node --ros-args --params-file config/keyop_params.yaml

Dashing:

ros2 run kobuki_keyop kobuki_keyop_node --ros-args __params:=config/keyop_params.yaml

[KadynCBR]

What do we think would be the way to replicate the safety launch?
run the keyop node and then have a second terminal with the launch handling the smoother and safety controller?

[stonier]

Probably a good first ros2 tutorial for kobuki_documentation.

And we should get it to the point where it doesn't need arguments, nor separate launchers to get smoothing / safety controll incorporated.