Mention gettext for user-defined strings

Author: tomasr8

Doc/howto/argparse.rst

@@ -815,7 +815,7 @@ For instance, in this :mod:`argparse` output:
      -q, --quiet
 
 The strings ``usage:``, ``positional arguments:``, ``options:`` and
-``show this help message and exit`` are all translatable.
+``show this help message and exit`` are all translatable. 
 
 In order to translate these strings, they must first be extracted
 into a ``.po`` file. For example, using `Babel <https://babel.pocoo.org/>`__,
@@ -839,6 +839,7 @@ Once the messages in the ``.po`` file are translated and the translations are
 installed using :mod:`gettext`, :mod:`argparse` will be able to display the
 translated messages.
 
+To translate your own strings in the :mod:`argparse` output, use :mod:`gettext`.
 
 Conclusion
 ==========