Update the translation guidelines, as the translation portal has been closed down.

CONTRIBUTE.md

@@ -133,9 +133,10 @@ You can find the list of security advisories we have published [here](https://si
 ## Translations
 
 SimpleSAMLphp is translated to many languages, though it needs constant updates from translators, as well as new
-translations to other languages. Translations can be contributed through [the translation portal](https://translation.rnd.feide.no/).
-You can also join the [translators mailing list](http://groups.google.com/group/simplesamlphp-translation) to keep up
-to date.
+translations to other languages. For the moment, translations can be contributed as **pull requests**. We are looking
+at better ways to translate the software that would make your life easier, so stay tuned! You can also join the
+[translators mailing list](http://groups.google.com/group/simplesamlphp-translation) to keep up to date on the
+latest news.
 
 Before starting a new translation, decide what style you want to use, whether you want to address the user in a polite
 manner or not, etc. Be coherent and keep that style through all your translations. If there is already a translation and