Reword superseded chapter intro

Author: ncoghlan

Doc/library/superseded.rst

@@ -9,7 +9,10 @@ for most use cases, and are retained primarily to preserve backwards compatibili
 
 Modules may appear in this chapter because they only cover a limited subset of
 a problem space, and a more generally applicable solution is available elsewhere
-in the standard library (for example, :mod:`getopt`).
+in the standard library (for example, :mod:`getopt` covers the very specific
+task of "mimic the C :c:func:`!getopt` API in Python", rather than the broader
+command line option parsing and argument parsing capabilities offered by
+:mod:`optparse` and :mod:`argparse`).
 
 Alternatively, modules may appear in this chapter because they are deprecated
 outright, and awaiting removal in a future release, or they are