Fix default from value docs

main.go

@@ -34,7 +34,7 @@ func main() {
 	flag.StringVar(&input, "i", "", "Read from a tar archive file, instead of STDIN")
 	flag.StringVar(&output, "o", "", "Write to a file, instead of STDOUT")
 	flag.StringVar(&tag, "t", "", "Repository name and tag for new image")
-	flag.StringVar(&from, "from", "", "Squash from layer ID (default is root)")
+	flag.StringVar(&from, "from", "", "Squash from layer ID (default: first FROM layer)")
 	flag.BoolVar(&keepTemp, "keepTemp", false, "Keep temp dir when done. (Useful for debugging)")
 	flag.BoolVar(&verbose, "verbose", false, "Enable verbose logging")
 	flag.BoolVar(&version, "v", false, "Print version information and quit")