Merge pull request #919 from zhaoleidd/fix_ps_argument_manual

Fix ps argument manual

Author: Mrunal Patel

man/runc-ps.8.md

@@ -2,7 +2,7 @@
    runc ps - ps displays the processes running inside a container
 
 # SYNOPSIS
-   runc ps [command options] <container-id> <ps options>
+   runc ps [command options] <container-id> [ps options]
 
 # OPTIONS
    --format value, -f value     select one of: table(default) or json

ps.go

@@ -16,7 +16,7 @@ import (
 var psCommand = cli.Command{
 	Name:      "ps",
 	Usage:     "ps displays the processes running inside a container",
-	ArgsUsage: `<container-id> <ps options>`,
+	ArgsUsage: `<container-id> [ps options]`,
 	Flags: []cli.Flag{
 		cli.StringFlag{
 			Name:  "format, f",