Add whatsnew entry

Author: makbigc

doc/source/whatsnew/v0.25.0.rst

@@ -274,7 +274,7 @@ Datetimelike
 - Bug in :class:`DataFrame` and :class:`Series` where timezone aware data with ``dtype='datetime64[ns]`` was not cast to naive (:issue:`25843`)
 - Improved :class:`Timestamp` type checking in various datetime functions to prevent exceptions when using a subclassed ``datetime`` (:issue:`25851`)
 - Bug in :class:`Series` and :class:`DataFrame` repr where ``np.datetime64('NaT')`` and ``np.timedelta64('NaT')`` with ``dtype=object`` would be represented as ``NaN`` (:issue:`25445`)
--
+- Bug in adding :class:`DateOffset` with nonzero month to :class:`DatetimeIndex` would raise ``ValueError`` (:issue:`26258`)
 
 Timedelta
 ^^^^^^^^^