dockerimg: use emoji in container debug info

This should potentially be removed (or moved to --verbose) but I am
still using it semi-reguarly during debugging.
Should probably be removed in a few weeks by default.
diff --git a/dockerimg/dockerimg.go b/dockerimg/dockerimg.go
index 22dfa45..d812987 100644
--- a/dockerimg/dockerimg.go
+++ b/dockerimg/dockerimg.go
@@ -196,7 +196,7 @@
 		return fmt.Errorf("docker cp: %s, %w", out, err)
 	}
 
-	fmt.Printf("starting container %s\n", cntrName)
+	fmt.Printf("📦 running in container %s\n", cntrName)
 
 	// Start the sketch container
 	if out, err := combinedOutput(ctx, "docker", "start", cntrName); err != nil {