pythonGH-108009: Add clarification of parser and argument defaults in argparse docs (python#124154)

Co-authored-by: C.A.M. Gerlach <[email protected]>

Author: savannahostrowski

Doc/library/argparse.rst

@@ -2070,7 +2070,9 @@ Parser defaults
      >>> parser.parse_args(['736'])
      Namespace(bar=42, baz='badger', foo=736)
 
-   Note that parser-level defaults always override argument-level defaults::
+   Note that defaults can be set at both the parser level using :meth:`set_defaults`
+   and at the argument level using :meth:`add_argument`. If both are called for the
+   same argument, the last default set for an argument is used::
 
      >>> parser = argparse.ArgumentParser()
      >>> parser.add_argument('--foo', default='bar')