added whatsnew note in the performance section

Author: anmyachev

doc/source/whatsnew/v0.25.0.rst

@@ -288,6 +288,7 @@ Performance Improvements
 - Improved performance of :meth:`Series.map` for dictionary mappers on categorical series by mapping the categories instead of mapping all values (:issue:`23785`)
 - Improved performance of :meth:`read_csv` by faster concatenating date columns without extra conversion to string for integer/float zero
   and float NaN; by faster checking the string for the possibility of being a date (:issue:`25754`)
+- For :meth:`to_datetime` changed default value of cache parameter to ``True`` (:issue:`26043`)
 
 .. _whatsnew_0250.bug_fixes: