Documentation on usage of gazebo simulation

[urmahp]

Feature summary

We should let people now that the robot can be simulated with the gazebo repository or the ignition repository.

Adding the documentation in the usage documentation of this driver would add more awareness on different ways to simulate your solution before testing it on real hardware. I therefore suggest to add a section in the usage documentation where we explain gazebo/ignition simulation and a description on how to set it up or a link to the repository with a description on how to set it up.