add note about cloudpickle to whatsnew

docs/source/whatsnew/pr/cloudpickle.rst

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+* Adds a ``use_cloudpickle`` method to ``DirectView`` objects, which works like
+  ``view.use_dill()``, but causes the ``cloudpickle`` module from PiCloud's
+  `cloud`__ library to be used rather than dill or the builtin pickle module.
+
+  __ https://pypi.python.org/pypi/cloud