[Notifier] Add a missing reference link

Author: javiereguiluz

notifier.rst

@@ -1089,6 +1089,7 @@ is dispatched. Listeners receive a
 .. _`RocketChat`: https://github.com/symfony/symfony/blob/{version}/src/Symfony/Component/Notifier/Bridge/RocketChat/README.md
 .. _`SMSFactor`: https://github.com/symfony/symfony/blob/{version}/src/Symfony/Component/Notifier/Bridge/SmsFactor/README.md
 .. _`Sendberry`: https://github.com/symfony/symfony/blob/{version}/src/Symfony/Component/Notifier/Bridge/Sendberry/README.md
+.. _`Sendinblue`: https://github.com/symfony/symfony/blob/{version}/src/Symfony/Component/Notifier/Bridge/Sendinblue/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
 .. _`Slack`: https://github.com/symfony/symfony/blob/{version}/src/Symfony/Component/Notifier/Bridge/Slack/README.md