Add docs how to adjust MTU size of the docker network (#6779)

Signed-off-by: Lorenzo Moscati <lorenzo@moscati.page>

compose.yaml

@@ -7,7 +7,8 @@ services:
     volumes:
       - nextcloud_aio_mastercontainer:/mnt/docker-aio-config # This line is not allowed to be changed as otherwise the built-in backup solution will not work
       - /var/run/docker.sock:/var/run/docker.sock:ro # May be changed on macOS, Windows or docker rootless. See the applicable documentation. If adjusting, don't forget to also set 'WATCHTOWER_DOCKER_SOCKET_PATH'!
-    network_mode: bridge # add to the same network as docker run would do
+    network_mode: bridge # This adds the container to the same network as docker run would do. Comment this line and uncomment the line below and the networks section at the end of the file if you want to define a custom MTU size for the docker network
+    # networks: ["nextcloud-aio"]
     ports:
       - 80:80 # Can be removed when running behind a web server or reverse proxy (like Apache, Nginx, Caddy, Cloudflare Tunnel and else). See https://github.com/nextcloud/all-in-one/blob/main/reverse-proxy.md
       - 8080:8080
@@ -69,3 +70,10 @@ volumes: # If you want to store the data on a different drive, see https://githu
   # caddy_config:
   # caddy_data:
   # caddy_sites:
+
+# # Adjust the MTU size of the docker network. See https://github.com/nextcloud/all-in-one#how-to-adjust-the-mtu-size-of-the-docker-network
+# networks:
+#   nextcloud-aio:
+#     name: nextcloud-aio
+#     driver_opts:
+#       com.docker.network.driver.mtu: 1440