DOC: Add links to zenodo datasets in fetcher script description

Add the zenodo places where the datasets dwell to the fetcher script
description so that they are shown when the help is shown.

scripts/fetch_data.py

@@ -10,7 +10,9 @@
 def _build_arg_parser():
 
     parser = argparse.ArgumentParser(
-        description="Fetch tractolearn dataset",
+        description="Fetch tractolearn dataset. The datasets are available at "
+                    "https://doi.org/10.5281/zenodo.7562790 and "
+                    "https://doi.org/10.5281/zenodo.7562635",
         formatter_class=argparse.ArgumentDefaultsHelpFormatter,
     )
     parser.add_argument(