Clarify robotName semantics

[traversaro]

We should clarify in documentation the meaning of robotName, that is just the portprefix, so it can be ignored by YARP-less Simulink models, see

wb-toolbox/toolbox/base/src/RobotInterface.cpp

Line 175 in b776e49

for (auto cb : config.getControlBoardsNames()) {

.

fyi @VenusPasandi