Update the description of the TypeError exception regarding freezing instances

Author: tangyuan0821

Doc/library/dataclasses.rst

@@ -164,8 +164,8 @@ Module contents
      generate an exception.  This emulates read-only frozen instances.
      See the :ref:`discussion <dataclasses-frozen>` below.
 
-     If :meth:`~object.__setattr__` or :meth:`~object.__delattr__` is defined in the class,
-     then :exc:`TypeError` is raised.
+     If :meth:`~object.__setattr__` or :meth:`~object.__delattr__` is defined in the class
+     and *frozen* is true, then :exc:`TypeError` is raised.
 
    - *match_args*: If true (the default is ``True``), the
      :attr:`~object.__match_args__` tuple will be created from the list of