Add Discord notifier

Author: mpiot

notifier.rst

@@ -131,11 +131,12 @@ Slack       ``symfony/slack-notifier``       ``slack://default/ID``
 Telegram    ``symfony/telegram-notifier``    ``telegram://TOKEN@default?channel=CHAT_ID``
 Mattermost  ``symfony/mattermost-notifier``  ``mattermost://TOKEN@ENDPOINT?channel=CHANNEL``
 RocketChat  ``symfony/rocketchat-notifier``  ``rocketchat://TOKEN@ENDPOINT?channel=CHANNEL``
+Discord    ``symfony/discord-notifier``      ``discord://TOKEN@default?channel=ID``
 ==========  ===============================  ============================================
 
 .. versionadded:: 5.1
 
-    The Mattermost and RocketChat integrations were introduced in Symfony
+    The Mattermost, RocketChat and Discord integrations were introduced in Symfony
     5.1. The Slack DSN changed in Symfony 5.1 to use Slack Incoming
     Webhooks instead of legacy tokens.
 
@@ -293,7 +294,7 @@ transport:
                         %env(SLACK_DSN)% || %env(TELEGRAM_DSN)%
                     </framework:chatter-transport>
 
-                    <!-- Send notifications to the next scheduled transport 
+                    <!-- Send notifications to the next scheduled transport
                          calculated by round robin -->
                     <framework:chatter-transport name="slack">
                         %env(SLACK_DSN)% && %env(TELEGRAM_DSN)%