Add Docker stats to runtime metrics article

Fixes #13170

Signed-off-by: Ankush Agarwal <ankushagarwal11@gmail.com>

docs/articles/runmetrics.md

@@ -2,7 +2,7 @@
 +++
 title = "Runtime metrics"
 description = "Measure the behavior of running containers"
-keywords = ["docker, metrics, CPU, memory, disk, IO, run,  runtime"]
+keywords = ["docker, metrics, CPU, memory, disk, IO, run,  runtime, stats"]
 [menu.main]
 parent = "smn_administrate"
 weight = 4
@@ -11,6 +11,26 @@ weight = 4
 
 # Runtime metrics
 
+
+## Docker stats
+
+You can use the `docker stats` command to live stream a container's
+runtime metrics. The command supports CPU, memory usage, memory limit,
+and network IO metrics.
+
+The following is a sample output from the `docker stats` command
+
+    $ docker stats redis1 redis2
+    CONTAINER           CPU %               MEM USAGE/LIMIT     MEM %               NET I/O
+    redis1              0.07%               796 KB/64 MB        1.21%               788 B/648 B
+    redis2              0.07%               2.746 MB/64 MB      4.29%               1.266 KB/648 B
+
+
+The [docker stats](/reference/commandline/stats/) reference page has
+more details about the `docker stats` command. 
+
+## Control groups
+
 Linux Containers rely on [control groups](
 https://www.kernel.org/doc/Documentation/cgroups/cgroups.txt)
 which not only track groups of processes, but also expose metrics about
@@ -18,8 +38,6 @@ CPU, memory, and block I/O usage. You can access those metrics and
 obtain network usage metrics as well. This is relevant for "pure" LXC
 containers, as well as for Docker containers.
 
-## Control groups
-
 Control groups are exposed through a pseudo-filesystem. In recent
 distros, you should find this filesystem under `/sys/fs/cgroup`. Under
 that directory, you will see multiple sub-directories, called devices,