Update README.md

README.md

 
 In case you prefer using Docker:
 
-You need to install docker on your server first.
+You need to install docker on your server first (see [https://docs.docker.com/install/linux/docker-ce/debian/](here))
 Make sure `docker.service` is started correctly.
 
+    systemctl status docker.service
+
 **If you want to use the latest stable image: **
 
     sudo docker run \