Translation README for Python GTK+ 3 Tutorial

[Rafael Fontenelle <rafaelff gnome org>]

Hi all,

I may have noticed the Python GTK+ 3 Tutorial[1] now has a module
named pygobject-tutorial[2] in D-L for translation. Just wanted to let
you know there is a Translation README [3] that might come in handy
for those interested in testing the translation or wondering how to
submit the translation.

Hope it helps!

[1] https://python-gtk-3-tutorial.readthedocs.io/
[2] https://l10n.gnome.org/module/pygobject-tutorial/
[3] https://github.com/sebp/PyGObject-Tutorial/tree/master/translations

Best regards,
Rafael Fontenele