[3.13] gh-141004: Document PySuper_Type (GH-141315) (GH-141319)

gh-141004: Document `PySuper_Type` (GH-141315)
(cherry picked from commit 14c6222)

Co-authored-by: Stan Ulbrych <89152624+StanFromIreland@users.noreply.github.com>

Author: miss-islington

Doc/c-api/descriptor.rst

@@ -43,6 +43,12 @@ found in the dictionary of type objects.
 Built-in descriptors
 ^^^^^^^^^^^^^^^^^^^^
 
+.. c:var:: PyTypeObject PySuper_Type
+
+   The type object for super objects. This is the same object as
+   :class:`super` in the Python layer.
+
+
 .. c:var:: PyTypeObject PyClassMethod_Type
 
    The type of class method objects. This is the same object as