Also reword What's New entry

Author: ncoghlan

Doc/whatsnew/3.13.rst

@@ -1656,8 +1656,12 @@ optparse
   aren't using a third party command line argument processing
   library, there are aspects of the way ``argparse`` works that
   mean the lower level ``optparse`` module may provide a better
-  foundation for *writing* argument processing libraries.
-  (Contributed by Alyssa Coghlan in :gh:`126180`.)
+  foundation for *writing* argument processing libraries, and
+  for implementing command line applications which adhere more
+  strictly than ``argparse`` does to various Unix command line
+  processing conventions that originate in the behaviour of the
+  C :c:func:`getopt` function .
+  (Contributed by Alyssa Coghlan and Serhiy Storchaka in :gh:`126180`.)
 
 
 pathlib