Update reference documentation

Signed-off-by: Silvin Lubecki <silvin.lubecki@docker.com>
Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

docs/reference/commandline/volume_ls.md

@@ -20,7 +20,12 @@ Options:
                        - driver=<string> a volume's driver name
                        - label=<key> or label=<key>=<value>
                        - name=<string> a volume's name
-      --format string  Pretty-print volumes using a Go template
+      --format string  Format output using a custom template:
+                       'table':            Print output in table format with column headers (default)
+                       'table TEMPLATE':   Print output in table format using the given Go template
+                       'json':             Print in JSON format
+                       'TEMPLATE':         Print output using the given Go template.
+                       Refer to https://docs.docker.com/go/formatting/ for more information about formatting output with templates
       --help           Print usage
   -q, --quiet          Only display volume names
 ```
@@ -182,6 +187,12 @@ vol2: local
 vol3: local
 ```
 
+To list all volumes in JSON format, use the `json` directive:
+```console
+$ docker volume ls --format json
+{"Driver":"local","Labels":"","Links":"N/A","Mountpoint":"/var/lib/docker/volumes/docker-cli-dev-cache/_data","Name":"docker-cli-dev-cache","Scope":"local","Size":"N/A"}
+```
+
 ## Related commands
 
 * [volume create](volume_create.md)