DOC: timezone warning for dates beyond TODAY (#34100)

* DOC: timezone warning for dates beyond TODAY

introducing a suggestion discussed in PR #33863 :
Added a warning in the user guide that timezone conversion on future dates is inherently unreliable.

* shorter warning text

Co-authored-by: Marco Gorelli <[email protected]>

Author: joooeey

doc/source/user_guide/timeseries.rst

@@ -2319,13 +2319,18 @@ you can use the ``tz_convert`` method.
     Instead, the datetime needs to be localized using the ``localize`` method
     on the ``pytz`` time zone object.
 
+.. warning::
+
+    Be aware that for times in the future, correct conversion between time zones
+    (and UTC) cannot be guaranteed by any time zone library because a timezone's
+    offset from UTC may be changed by the respective government.
+
 .. warning::
 
     If you are using dates beyond 2038-01-18, due to current deficiencies
     in the underlying libraries caused by the year 2038 problem, daylight saving time (DST) adjustments
     to timezone aware dates will not be applied. If and when the underlying libraries are fixed,
-    the DST transitions will be applied. It should be noted though, that time zone data for far future time zones
-    are likely to be inaccurate, as they are simple extrapolations of the current set of (regularly revised) rules.
+    the DST transitions will be applied.
 
     For example, for two dates that are in British Summer Time (and so would normally be GMT+1), both the following asserts evaluate as true: