Mention that 'w' is not supported

Author: tomasr8

Doc/library/multiprocessing.rst

@@ -1560,12 +1560,13 @@ inherited by child processes.
 
    *typecode_or_type* determines the type of the elements of the returned array:
    it is either a :ref:`ctypes type <ctypes-fundamental-data-types>` or a one
-   character typecode of the kind used by the :mod:`array` module.  In addition,
-   the ``'c'`` typecode is an alias for :class:`ctypes.c_char`.  If
-   *size_or_initializer* is an integer, then it determines the length of the
-   array, and the array will be initially zeroed. Otherwise,
-   *size_or_initializer* is a sequence which is used to initialize the array
-   and whose length determines the length of the array.
+   character typecode of the kind used by the :mod:`array` module with the
+   exception of ``'w'``, which is not supported.  In addition, the ``'c'``
+   typecode is an alias for :class:`ctypes.c_char`.  If *size_or_initializer*
+   is an integer, then it determines the length of the array, and the array
+   will be initially zeroed. Otherwise, *size_or_initializer* is a sequence
+   which is used to initialize the array and whose length determines the length
+   of the array.
 
    If *lock* is ``True`` (the default) then a new lock object is created to
    synchronize access to the value.  If *lock* is a :class:`Lock` or