docs: add typerror exception to active_branch method

Author: Patrick Gerard

git/repo/base.py

@@ -858,6 +858,8 @@ def ignored(self, *paths: PathLike) -> List[str]:
     @property
     def active_branch(self) -> Head:
         """The name of the currently active branch.
+
+        Raises:	TypeError – If HEAD is detached
         :return: Head to the active branch"""
         # reveal_type(self.head.reference)  # => Reference
         return self.head.reference