Added a whatsnew entry for issue pandas-dev#18581

Author: dhirschfeld

doc/source/whatsnew/v0.22.0.txt

@@ -77,6 +77,7 @@ Other Enhancements
 - :func:`Series.fillna` now accepts a Series or a dict as a ``value`` for a categorical dtype (:issue:`17033`)
 - :func:`pandas.read_clipboard` updated to use qtpy, falling back to PyQt5 and then PyQt4, adding compatibility with Python3 and multiple python-qt bindings (:issue:`17722`)
 - Improved wording of ``ValueError`` raised in :func:`read_csv` when the ``usecols`` argument cannot match all columns. (:issue:`17301`)
+- Enabled the use of non-default indexes in ``to_parquet`` with pyarrow>=0.7.0 (:issue:`18581`)
 
 .. _whatsnew_0220.api_breaking: