Make reference to Generic Attribute Management a hyperlink.

Doc/extending/newtypes.rst

@@ -446,7 +446,7 @@ and put the definitions in the :attr:`tp_members` slot::
    Noddy_members,             /* tp_members */
 
 Each member definition has a member name, type, offset, access flags and
-documentation string. See the "Generic Attribute Management" section below for
+documentation string. See the :ref:`Generic-Attribute-Management` section below for
 details.
 
 A disadvantage of this approach is that it doesn't provide a way to restrict the
@@ -1129,6 +1129,8 @@ disappeared starting with Python 2.2, though there are many examples which have
 not been updated to use some of the new generic mechanism that is available.
 
 
+.. _generic-attribute-management:
+
 Generic Attribute Management
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^