Add ntfy push notifications + mailrise SMTP bridge

- ntfy: self-hosted push notification service (port 8086)
- mailrise: SMTP-to-ntfy converter (port 8025)
- Configs in ./ntfy/server.yml and ./ntfy/mailrise.yml
- Token-based authentication for ntfy
- Updated docs and .gitignore

ntfy/mailrise.yml

@@ -0,0 +1,13 @@
+smtp:
+  hostname: mailrise
+  port: 8025
+
+ntfy:
+  default:
+    url: http://ntfy:8086
+    token: tk_yourtokenhere
+
+configs:
+  alerts: alerts
+  backups: backups
+  paperless: paperless