Print elapsed time for image unpack

The provides additional insight into how much time is being spent in
unpacking and is helpful in performance comparison for just this stage
without resorting to running under time command in linux for example.

Signed-off-by: Alakesh Haloi <alakeshh@amazon.com>

cmd/ctr/commands/images/pull.go

@@ -19,6 +19,7 @@ package images
 import (
 	"fmt"
 	"net/http/httptrace"
+	"time"
 
 	"github.com/containerd/containerd"
 	"github.com/containerd/containerd/cmd/ctr/commands"
@@ -124,6 +125,7 @@ command. As part of this process, we do the following:
 			p = append(p, platforms.DefaultSpec())
 		}
 
+		start := time.Now()
 		for _, platform := range p {
 			fmt.Printf("unpacking %s %s...\n", platforms.Format(platform), img.Target.Digest)
 			i := containerd.NewImageWithPlatform(client, img, platforms.Only(platform))
@@ -140,8 +142,7 @@ command. As part of this process, we do the following:
 				fmt.Printf("image chain ID: %s\n", chainID)
 			}
 		}
-
-		fmt.Println("done")
+		fmt.Printf("done: %s\t\n", time.Since(start))
 		return nil
 	},
 }