move whatsnew note to parquet section

Author: jorisvandenbossche

doc/source/whatsnew/v0.21.1.txt

@@ -61,6 +61,9 @@ New features
 Improvements to the Parquet IO functionality
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
+- :func:`DataFrame.to_parquet` will now write non-default indexes when the
+  underlying engine supports it. The indexes will be preserved when reading
+  back in with :func:`read_parquet` (:issue:`18581`).
 - :func:`read_parquet` now allows to specify the columns to read from a parquet file (:issue:`18154`)
 - :func:`read_parquet` now allows to specify kwargs which are passed to the respective engine (:issue:`18216`)
 
@@ -71,7 +74,6 @@ Other Enhancements
 
 - :meth:`Timestamp.timestamp` is now available in Python 2.7. (:issue:`17329`)
 - :class:`Grouper` and :class:`TimeGrouper` now have a friendly repr output (:issue:`18203`).
-- Enabled the use of non-default indexes in :func:`DataFrame.to_parquet` where the underlying engine supports it (:issue:`18581`)
 
 .. _whatsnew_0211.deprecations:
 

doc/source/whatsnew/v0.22.0.txt

@@ -329,4 +329,4 @@ Other
 ^^^^^
 
 - Improved error message when attempting to use a Python keyword as an identifier in a ``numexpr`` backed query (:issue:`18221`)
-- 
+-