Make the README robot-agnostic

[xEnVrE]

I noticed that in the section https://github.com/robotology/yarp-device-realsense2#from-the-command-line the README suggests exporting YARP_ROBOT_NAME to either CER01, CER02 or CER03.

It seems to me that this suggestion might be confusing as the repository is about using the realsense with YARP, not necessarily with the R1 robot.

What do you think? Would it be possible to remove these instructions or, at least, move in a separate note later on in the README?

Thank you

[traversaro]

I guess it make sense. We could just explain how to write an ad hoc configuration file and just launch it via yarpdev by running yarpdev in the same directory of the newly created configuration file. Only later we can explain that if you use R1 or iCub robots, robots-configuration contains this configuration files and how to use it. Feel free to submit a PR with these changes, thanks!