DOC: Update whatsnew about NDFrame._dir_additions enhancements (pandas-dev#16326, pandas-dev#18587)

Author: Martin Journois

doc/source/whatsnew/v0.22.0.txt

@@ -135,7 +135,7 @@ Other Enhancements
 - Improved wording of ``ValueError`` raised in :func:`read_csv` when the ``usecols`` argument cannot match all columns. (:issue:`17301`)
 - :func:`DataFrame.corrwith` now silently drops non-numeric columns when passed a Series. Before, an exception was raised (:issue:`18570`).
 - :class:`IntervalIndex` now supports time zone aware ``Interval`` objects (:issue:`18537`, :issue:`18538`)
-
+- :func:`Series` / :func:`DataFrame` tab completion also returns identifiers in the first level of a :func:`MultiIndex`. (:issue:`16326`)
 
 .. _whatsnew_0220.api_breaking:
 
@@ -230,6 +230,7 @@ Performance Improvements
 - Improved performance of :func:`Series.dt.date` and :func:`DatetimeIndex.date` (:issue:`18058`)
 - Improved performance of :func:`IntervalIndex.symmetric_difference()` (:issue:`18475`)
 - Improved performance of ``DatetimeIndex`` and ``Series`` arithmetic operations with Business-Month and Business-Quarter frequencies (:issue:`18489`)
+- :func:`Series` / :func:`DataFrame` tab completion limits to 100 values, for better performance. (:issue:`18587`)
 
 .. _whatsnew_0220.docs: