Add Zenodo links to the fetch data

[fdumais]

We should add the Zenodo links to the fetch_data / describing in more details each file downloaded

[jhlegarreta]

A few notes:

• Python does not support well documenting the enum in https://github.com/scil-vital/tractolearn/blob/main/tractolearn/tractoio/dataset_fetch.py#L23

  I did not find a solution after spending some time. That would be the best place to document each dataset.

• Not sure whether/how these tuples would appear in the documentation:
  https://github.com/scil-vital/tractolearn/blob/main/tractolearn/tractoio/dataset_fetch.py#L325

But they contain the descriptions mentioned in the issue. Another possibility would be to add a method (and a script if necessary; or call such a method from the fetcher script description if that is doable) that will go over each tuple and that will print the description item.

If you need to add a description in zenodo, I'd copy and paste those descriptions to avoid getting them out-of-sync.

[jhlegarreta]

Another possibility would be to add a method (and a script if necessary; or call such a method from the fetcher script description if that is doable) that will go over each tuple and that will print the description item.

#48 implements that solution.