Reference xarray_extras for csv writing.

Author: dcherian

doc/io.rst

@@ -744,6 +744,9 @@ Formats supported by Pandas
 
 For more options (tabular formats and CSV files in particular), consider
 exporting your objects to pandas and using its broad range of `IO tools`_.
+For CSV files, one might also consider `xarray_extras.csv.to_csv()`_.
+
+.. _xarray_extras: https://xarray-extras.readthedocs.io/en/latest/api/csv.html
 
 .. _IO tools: http://pandas.pydata.org/pandas-docs/stable/io.html