Polyhedron_demo: Make video tutorials

[maxGimeno]

Issue Details

We should make youtube videos to demonstrate the features of the demo, like video tutos.

[sgiraudot]

For the record, GeometryFactory has a Youtube channel with few videos on it (the latest is the one I made for classification). The issue is still valid as we probably need more explicit and detailed videos.

(Note that as I have a small experience with some video processing software, I can help.)