Add a whatsnew note

Author: makbigc

doc/source/whatsnew/v0.25.0.rst

@@ -176,7 +176,8 @@ Performance Improvements
   int8/int16/int32 and the searched key is within the integer bounds for the dtype (:issue:`22034`)
 - Improved performance of :meth:`pandas.core.groupby.GroupBy.quantile` (:issue:`20405`)
 - Improved performance of :meth:`read_csv` by faster tokenizing and faster parsing of small float numbers (:issue:`25784`)
-
+- Imporved performance of :meth:`IntervalIndex.is_monotonic`, :meth:`IntervalIndex.is_monotonic_increasing` and :meth:`IntervalIndex.is_monotonic_decreasing` by removing conversion to :class:`MultiIndex` (:issue:`24813`)
+  
 .. _whatsnew_0250.bug_fixes:
 
 Bug Fixes