Note argparse exit code in documentation (GH-119568)

Co-authored-by: Savannah Ostrowski <[email protected]>

Doc/library/argparse.rst

@@ -541,7 +541,8 @@ exit_on_error
 ^^^^^^^^^^^^^
 
 Normally, when you pass an invalid argument list to the :meth:`~ArgumentParser.parse_args`
-method of an :class:`ArgumentParser`, it will exit with error info.
+method of an :class:`ArgumentParser`, it will print a *message* to :data:`sys.stderr` and exit with a status
+code of 2.
 
 If the user would like to catch errors manually, the feature can be enabled by setting
 ``exit_on_error`` to ``False``::