Add comment to link rationale for existence.

Author: jaraco

importlib_metadata/_meta.py

@@ -18,6 +18,7 @@ def __getitem__(self, key: str) -> str:
     def __iter__(self) -> Iterator[str]:
         ...  # pragma: no cover
 
+    # overload per python/importlib_metadata#435
     @overload
     def get_all(self, name: str, failobj: None = None) -> Optional[List[Any]]:
         ...