add rollback explanation to docker service update command document
@@ -154,6 +154,51 @@ $ docker service update --mount-rm /somewhere myservice
myservice
```
+### Rolling back to the previous version of a service
+
+Use the `--rollback` option to roll back to the previous version of the service.
+
+This will revert the service to the configuration that was in place before the most recent `docker service update` command.
+
+The following example updates the number of replicas for the service from 4 to 5, and then rolls back to the previous configuration.
+
+```bash
+$ docker service update --replicas=5 web
+
+web
+
+$ docker service ls
+
+ID NAME MODE REPLICAS IMAGE
+80bvrzp6vxf3 web replicated 0/5 nginx:alpine
+
+```
+Roll back the `web` service...
+
+```bash
+$ docker service update --rollback web
+
+web
+
+$ docker service ls
+
+ID NAME MODE REPLICAS IMAGE
+80bvrzp6vxf3 web replicated 0/4 nginx:alpine
+
+```
+
+Other options can be combined with `--rollback` as well, for example, `--update-delay 0s` to execute the rollback without a delay between tasks:
+
+```bash
+$ docker service update \
+ --rollback \
+ --update-delay 0s
+ web
+
+web
+
+```
+
### Add or remove secrets
Use the `--secret-add` or `--secret-rm` options add or remove a service's
