Added SERVER_NAME environment variable (pterodactyl#3110)

Added SERVER_NAME environment variable to stop laravel framework server name defaulting to localhost, causing mail relays such as Gmail to stop silently dropping emails due to sender name being localhost.

Author: aussieserverhosts

.env.example

@@ -25,6 +25,11 @@ MAIL_USERNAME=
 MAIL_PASSWORD=
 MAIL_ENCRYPTION=tls
 MAIL_FROM=no-reply@example.com
+# You should set this to your domain to prevent it defaulting to 'localhost', causing
+# mail servers such as Gmail to reject your mail.
+#
+# @see: https://github.com/pterodactyl/panel/pull/3110
+# SERVER_NAME=panel.yourdomain.com
 
 QUEUE_HIGH=high
 QUEUE_STANDARD=standard