Implemet docker update command

It's used for updating properties of one or more containers, we only
support resource configs for now. It can be extended in the future.

Signed-off-by: Qiang Huang <h.huangqiang@huawei.com>

docs/reference/commandline/index.md

@@ -59,6 +59,7 @@ You start the Docker daemon with the command line. How you start the daemon affe
 * [stop](stop.md)
 * [top](top.md)
 * [unpause](unpause.md)
+* [update](update.md)
 * [wait](wait.md)
 
 ### Hub and registry commands

docs/reference/commandline/update.md

@@ -0,0 +1,61 @@
+<!--[metadata]>
++++
+title = "update"
+description = "The update command description and usage"
+keywords = ["resources, update, dynamically"]
+[menu.main]
+parent = "smn_cli"
++++
+<![end-metadata]-->
+
+## update
+
+    Usage: docker update [OPTIONS] CONTAINER [CONTAINER...]
+
+    Updates container resource limits
+
+      --help=false               Print usage
+      --blkio-weight=0           Block IO (relative weight), between 10 and 1000
+      --cpu-shares=0             CPU shares (relative weight)
+      --cpu-period=0             Limit the CPU CFS (Completely Fair Scheduler) period
+      --cpu-quota=0              Limit the CPU CFS (Completely Fair Scheduler) quota
+      --cpuset-cpus=""           CPUs in which to allow execution (0-3, 0,1)
+      --cpuset-mems=""           Memory nodes (MEMs) in which to allow execution (0-3, 0,1)
+      -m, --memory=""            Memory limit
+      --memory-reservation=""    Memory soft limit
+      --memory-swap=""           Total memory (memory + swap), '-1' to disable swap
+      --kernel-memory=""         Kernel memory limit: container must be stopped
+
+The `docker update` command dynamically updates container resources.  Use this
+command to prevent containers from consuming too many resources from their
+Docker host.  With a single command, you can place limits on a single
+container or on many. To specify more than one container, provide
+space-separated list of container names or IDs.
+
+With the exception of the `--kernel-memory` value, you can specify these
+options on a running or a stopped container. You can only update
+`--kernel-memory` on a stopped container. When you run `docker update` on
+stopped container, the next time you restart it, the container uses those
+values.
+
+## EXAMPLES
+
+The following sections illustrate ways to use this command.
+
+### Update a container with cpu-shares=512
+
+To limit a container's cpu-shares to 512, first identify the container
+name or ID. You can use **docker ps** to find these values. You can also
+use the ID returned from the **docker run** command.  Then, do the following:
+
+```bash
+$ docker update --cpu-shares 512 abebf7571666
+```
+
+### Update a container with cpu-shares and memory
+
+To update multiple resource configurations for multiple containers:
+
+```bash
+$ docker update --cpu-shares 512 -m 300M abebf7571666 hopeful_morse
+```