Default installation instruction installs an iDynTree without irrlicht/visualizer support, but examples use irrlicht/visualizer

[traversaro]

The default installation procedure in the README will install idyntree from PyPI, but that version does not have irrlicht/visualizer support enabled (see robotology/robotology-superbuild#1012 (comment)).

However, I noticed that the example https://github.com/icub-tech-iit/urdf-modifiers/blob/23d5517413e1ce765ab5857130f0b30f588b0430/examples/stickBotModification.ipynb uses the iDynTree.Visualizer function, so it could be confusing for users that try to run it.

Probably we can try to modify the README to reflect what developers are actually using (so-called "dog-fooding"), that I guess is either:

• Install idyntree for conda-forge
• Install idyntree from source/robotology-superbuild

@Nicogene @GrmanRodriguez @CarlottaSartore

[traversaro]

I guess this was fixed by robotology/idyntree#1045 .