Add link for sipgate bridge

Author: sakul95

notifier.rst

@@ -1134,6 +1134,7 @@ is dispatched. Listeners receive a
 .. _`Seven.io`: https://github.com/symfony/symfony/blob/{version}/src/Symfony/Component/Notifier/Bridge/Sevenio/README.md
 .. _`SimpleTextin`: https://github.com/symfony/symfony/blob/{version}/src/Symfony/Component/Notifier/Bridge/SimpleTextin/README.md
 .. _`Sinch`: https://github.com/symfony/symfony/blob/{version}/src/Symfony/Component/Notifier/Bridge/Sinch/README.md
+.. _`Sipgate`: https://github.com/symfony/symfony/blob/{version}/src/Symfony/Component/Notifier/Bridge/Sipgate/README.md
 .. _`Slack`: https://github.com/symfony/symfony/blob/{version}/src/Symfony/Component/Notifier/Bridge/Slack/README.md
 .. _`Sms77`: https://github.com/symfony/symfony/blob/{version}/src/Symfony/Component/Notifier/Bridge/Sms77/README.md
 .. _`SmsBiuras`: https://github.com/symfony/symfony/blob/{version}/src/Symfony/Component/Notifier/Bridge/SmsBiuras/README.md