DOC: clarify (un)aware logic in tz_localize() docstring (pandas-dev#40940)

Author: jgehrcke

pandas/core/arrays/datetimes.py

@@ -855,8 +855,9 @@ def tz_localize(self, tz, ambiguous="raise", nonexistent="raise") -> DatetimeArr
         This method takes a time zone (tz) naive Datetime Array/Index object
         and makes this time zone aware. It does not move the time to another
         time zone.
-        Time zone localization helps to switch from time zone aware to time
-        zone unaware objects.
+
+        This method can also be used to do the inverse -- to create a time
+        zone unaware object from an aware object. To that end, pass `tz=None`.
 
         Parameters
         ----------