fix broken link

Author: wenh06

torch_ecg/databases/base.py

@@ -754,7 +754,7 @@ def helper(self, items: Union[List[str], str, type(None)] = None) -> None:
 
         References
         ----------
-        .. [#ann_man] https://archive.physionet.org/physiobank/annotations.shtml
+        .. [#ann_man] https://github.com/bemoody/lightwave/blob/master/client/doc/annotations.html
 
         """
         attrs = vars(self)