Improve error

x/examples/outline-connectivity/main.go

@@ -19,10 +19,12 @@ import (
 	"encoding/json"
 	"errors"
 	"flag"
+	"fmt"
 	"io"
 	"log"
 	"net"
 	"os"
+	"path"
 	"strings"
 	"time"
 
@@ -83,12 +85,19 @@ func unwrapAll(err error) error {
 	}
 }
 
+func init() {
+	flag.Usage = func() {
+		fmt.Fprintf(flag.CommandLine.Output(), "Usage: %s [flags...]\n", path.Base(os.Args[0]))
+		flag.PrintDefaults()
+	}
+}
+
 func main() {
 	verboseFlag := flag.Bool("v", false, "Enable debug output")
 	transportFlag := flag.String("transport", "", "Transport config")
 	domainFlag := flag.String("domain", "example.com.", "Domain name to resolve in the test")
 	resolverFlag := flag.String("resolver", "8.8.8.8,2001:4860:4860::8888", "Comma-separated list of addresses of DNS resolver to use for the test")
-	protoFlag := flag.String("proto", "tcp,udp", "Comma-separated list of the protocols to test. Muse be \"tcp\", \"udp\", or a combination of them")
+	protoFlag := flag.String("proto", "tcp,udp", "Comma-separated list of the protocols to test. Must be \"tcp\", \"udp\", or a combination of them")
 
 	flag.Parse()
 	if *verboseFlag {