Including line for docker swarm

To set it as provider

advanced/reverse-proxy/traefik.md

@@ -278,6 +278,7 @@ services:
       - --entrypoints.web.address=:80
       - --entrypoints.websecure.address=:443
       - --providers.docker=true
+      - --providers.swarm=true
       - --providers.docker.exposedbydefault=false
       - --providers.docker.network=public
       - --api