add CC-BY license, ensure responsible reuse in public domain

Hi all,

As you I presume realize this repository is public. The work is done, and the materials are still publicly available for participants and everybody. We could therefore also synchronize them to github (for better discoverability) and publish on zenodo (to make them even more indexed and citeable by doi). They might be as well useful to complement the future book.

For all this we would much benefit from a license choice.

@carlo.ferrigno (@ferrigno.carlo) clarified that the school funding imposes no restrictions on the license for these additional materials. So we can choose what we want.

I'd suggest CC-BY, the least restrictive of CC licenses. It only requires attribution - acknowledging that It is the one recommended by UNIGE for our work. But your funding agency might have a different opinion. You also might have a different option.

You may want to remove or add something (like an acknowledgement).

Please @g.raaijmakers93 @kate.alexander @floor.broekgaarden @sophie.lund.schroder @simone.bavera let us know what you think in the comments to this MR!

Cheers

Volodymyr