use uppercase letters for flag usage

Signed-off-by: panguicai008 <guicai.pan@daocloud.io>

cmd/ctr/commands/content/fetch.go

@@ -42,10 +42,10 @@ import (
 
 var fetchCommand = cli.Command{
 	Name:      "fetch",
-	Usage:     "fetch all content for an image into containerd",
+	Usage:     "Fetch all content for an image into containerd",
 	ArgsUsage: "[flags] <remote> <object>",
 	Description: `Fetch an image into containerd.
-	
+
 This command ensures that containerd has all the necessary resources to build
 an image's rootfs and convert the configuration to a runtime format supported
 by containerd.