Update mailer.rst

Mentioning `addBcc()` too.

Author: ThomasLandauer

mailer.rst

@@ -163,7 +163,7 @@ both strings or address objects::
     :class:`Symfony\\Component\\Mailer\\Event\\MessageEvent` event to set the
     same ``From`` email to all messages.
 
-Multiple addresses are defined with ``addTo()`` and ``addCc()``::
+Multiple addresses can be set with ``addTo()``, ``addCc()``, or ``addBcc()`::
 
     $email = (new Email())
         ->to('[email protected]')