Fixed #13661 -- Corrected example in the serialization docs. Thanks to jabapyth for the report.

``serializers.serialize()``, you provide a ``use_natural_keys=True``

argument::

    >>> serializers.serialize([book1, book2], format='json', indent=2, use_natural_keys=True)

    >>> serializers.serialize('json', [book1, book2], indent=2, use_natural_keys=True)

When ``use_natural_keys=True`` is specified, Django will use the

``natural_key()`` method to serialize any reference to objects of the