Missing licenses for data files

[santisoler]

Since the files under data live inside this repo, the CC-BY license extends to them as well. But I suspect some of those files might have different licenses, which can be compatible or incompatible with CC-BY (or even with CoCo).

It might be better to add the licenses for each one of the data files. We can add a README.md describing each data file together with the license under which they are distributed.

This is also a good opportunity to check if we are allowed to use these files inside CoCo 👀