Add CC0 license

[MakisH]

Similarly to the-teachingRSE-project/competencies#234.

@CaptainSifff you have a better overview of what else we may need to do. Together with @jlinx (initial commit), I am currently the only contributor in the Git history, so I don't think we need any further approvals.

Note that the website is based on https://github.com/mmistakes/minimal-mistakes, which is distributed under the MIT license. We still mention it in the footer.

This license is, of course, only for the content, not for the (minimal) technicalities.

Closes #7.

[CaptainSifff]

OK, I put some thought into it, and I'm wondering whether CC-BY is still a good idea... We are curating the resources of others. Awesome lists recommend CC-0 for that: https://github.com/sindresorhus/awesome/blob/main/awesome.md

[MakisH]

OK, I put some thought into it, and I'm wondering whether CC-BY is still a good idea... We are curating the resources of others. Awesome lists recommend CC-0 for that: https://github.com/sindresorhus/awesome/blob/main/awesome.md

I am fine with that as well.

[CaptainSifff]

CC0 by default should be fine. It could happen that in the future(maybe we have our own designed courses) that sub-parts of the website are on a different license.