readme update

README.md

@@ -39,6 +39,16 @@ docker run -d \
   centurylink/watchtower
 ```
 
+For private images:
+
+```
+docker run -d \
+  --name watchtower \
+  -e REPO_USER="username" -e REPO_PASS="pass" -e REPO_EMAIL="email" \
+  -v /var/run/docker.sock:/var/run/docker.sock \
+  drud/watchtower container_to_watch --debug
+```
+
 ### Arguments
 
 By default, watchtower will monitor all containers running within the Docker daemon to which it is pointed (in most cases this will be the local Docker daemon, but you can override it with the `--host` option described in the next section). However, you can restrict watchtower to monitoring a subset of the running containers by specifying the container names as arguments when launching watchtower.