bpo-38255: super() can search attributes as well as methods (GH-16368)

Improvement suggested by Géry Ogam.

Doc/library/functions.rst

@@ -1637,6 +1637,10 @@ are always available.  They are listed here in alphabetical order.
               super().method(arg)    # This does the same thing as:
                                      # super(C, self).method(arg)
 
+   In addition to method lookups, :func:`super` also works for attribute
+   lookups.  One possible use case for this is calling :term:`descriptor`\s
+   in a parent or sibling class.
+
    Note that :func:`super` is implemented as part of the binding process for
    explicit dotted attribute lookups such as ``super().__getitem__(name)``.
    It does so by implementing its own :meth:`__getattribute__` method for searching