bpo-47007: [doc] str special method lookup (GH-31863)

Clarify the `str()` docs to point out that `object.__str__()`
follows special method lookup.

Co-authored-by: Jelle Zijlstra <jelle.zijlstra@gmail.com>

Doc/library/stdtypes.rst

@@ -1517,7 +1517,8 @@ multiple fragments.
    depends on whether *encoding* or *errors* is given, as follows.
 
    If neither *encoding* nor *errors* is given, ``str(object)`` returns
-   :meth:`object.__str__() <object.__str__>`, which is the "informal" or nicely
+   :meth:`type(object).__str__(object) <object.__str__>`,
+   which is the "informal" or nicely
    printable string representation of *object*.  For string objects, this is
    the string itself.  If *object* does not have a :meth:`~object.__str__`
    method, then :func:`str` falls back to returning