gh-94300: Update datetime.strptime documentation (#95318)

The new wording better reflects the cases where `datetime.strptime` differs from` time.strptime`.

---------

Co-authored-by: Paul Ganssle <git@m.ganssle.io>

Author: howiezhao

Doc/library/datetime.rst

@@ -1043,7 +1043,7 @@ Other constructors, all class methods:
    Return a :class:`.datetime` corresponding to *date_string*, parsed according to
    *format*.
 
-   This is equivalent to::
+   If *format* does not contain microseconds or timezone information, this is equivalent to::
 
      datetime(*(time.strptime(date_string, format)[0:6]))