Update docker image must remove container (#148)

Author: bestlong

docs/getting-started/docker.md

@@ -169,7 +169,8 @@ is now as simple as
 ```
 $ docker pull nodered/node-red
 $ docker stop mynodered
-$ docker start mynodered
+$ docker rm mynodered
+$ docker run -it -p 1880:1880 -v node_red_user_data:/data --name mynodered nodered/node-red
 ```
 
 ### Docker Stack / Docker Compose