Add whats-new entry

Author: Zac-HD

doc/whats-new.rst

@@ -48,6 +48,9 @@ Bug fixes
 
 - Properly point :py:meth:`DataArray.__dask_scheduler__` to
   ``dask.threaded.get``.  By `Matthew Rocklin <https://github.com/mrocklin>`_.
+- Bug fixes in :py:meth:`DataArray.plot.imshow`: all-NaN arrays and arrays
+  with size one in some dimension can now be plotted, which is good for
+  exploring satellite imagery.  (:issue:`1780`)
 - Bug fixes in :py:meth:`DataArray.plot.imshow`: all-NaN arrays and arrays
   with size one in some dimension can now be plotted, which is good for
   exploring satellite imagery.  (:issue:`1780`)