Add doc for StaticMessage

Author: VincentLanglet

translation.rst

@@ -337,6 +337,14 @@ Templates are now much simpler because you can pass translatable objects to the
     There's also a :ref:`function called t() <reference-twig-function-t>`,
     available both in Twig and PHP, as a shortcut to create translatable objects.
 
+On the contrary, if you want your message to never be translated, you can
+ensure this behavior with the
+:class:`Symfony\\Component\\Translation\\StaticMessage` class::
+
+    use Symfony\Component\Translation\StaticMessage;
+
+    $message = new StaticMessage('This message will never by translated.');
+
 .. _translation-in-templates:
 
 Translations in Templates