add replicated in service scale command description

Signed-off-by: allencloud <allen.sun@daocloud.io>

contrib/completion/zsh/_docker

@@ -1075,7 +1075,7 @@ __docker_service_commands() {
         "inspect:Display detailed information on one or more services"
         "ls:List services"
         "rm:Remove one or more services"
-        "scale:Scale one or multiple services"
+        "scale:Scale one or multiple replicated services"
         "ps:List the tasks of a service"
         "update:Update a service"
     )

docs/reference/commandline/service_scale.md

@@ -18,7 +18,7 @@ keywords: ["service, scale"]
 ```markdown
 Usage:  docker service scale SERVICE=REPLICAS [SERVICE=REPLICAS...]
 
-Scale one or multiple services
+Scale one or multiple replicated services
 
 Options:
       --help   Print usage
@@ -28,8 +28,9 @@ Options:
 
 ### Scale a service
 
-The scale command enables you to scale one or more services either up or down to
-the desired number of replicas. The command will return immediately, but the
+The scale command enables you to scale one or more replicated services either up 
+or down to the desired number of replicas. This command cannot be applied on 
+services which are global mode. The command will return immediately, but the
 actual scaling of the service may take some time. To stop all replicas of a
 service while keeping the service active in the swarm you can set the scale to 0.
 
@@ -40,6 +41,15 @@ $ docker service scale frontend=50
 frontend scaled to 50
 ```
 
+The following command tries to scale a global service to 10 tasks and returns an error.
+
+```
+$ docker service create --mode global --name backend backend:latest
+b4g08uwuairexjub6ome6usqh
+$ docker service scale backend=10
+backend: scale can only be used with replicated mode
+```
+
 Directly afterwards, run `docker service ls`, to see the actual number of
 replicas.