[3.11] gh-98378: Add small format string example to strftime comments (GH-98379) (#98395)

gh-98378: Add small format string example to strftime comments (GH-98379)

A small example of what a full date and time would look like would help a lot of developers who may not realize that they should investigate `time.h`'s `strftime`, run `man strftime`, or click through a series of docs on the python docs before they get to the actual [definition here](https://docs.python.org/3/library/datetime.htmlGH-strftime-and-strptime-format-codes) which still doesn't have an obvious copy-pastable example of "what the heck format does this thing actually expect?".

Automerge-Triggered-By: GH:rhettinger
(cherry picked from commit 6ccca69d0d)

Co-authored-by: Alex Zvorygin <grafetu@gmail.com>

Co-authored-by: Alex Zvorygin <grafetu@gmail.com>
Co-authored-by: Alex Waygood <Alex.Waygood@Gmail.com>

Lib/datetime.py

@@ -1030,7 +1030,11 @@ class date:
             self._day, self._year)
 
     def strftime(self, fmt):
-        "Format using strftime()."
+        """
+        Format using strftime().
+
+        Example: "%d/%m/%Y, %H:%M:%S"
+        """
         return _wrap_strftime(self, fmt, self.timetuple())
 
     def __format__(self, fmt):