main: fix the output if a wrong or none command provided

Signed-off-by: Vincent Batts <vbatts@hashbangbash.com>

main.go

@@ -15,12 +15,11 @@ import (
 func main() {
 	cmd := &cli.Command{
 		Name:    "too-soon",
-		Usage:   "check if something expires too soon",
+		Usage:   "check if certificates expire too soon",
 		Version: "0.1",
 		Authors: []any{
 			&mail.Address{Name: "Vincent Batts", Address: "vbatts@hashbangbash.com"},
 		},
-		DefaultCommand: "pem",
 		Flags: []cli.Flag{
 			&cli.IntFlag{
 				Name:  "days",
@@ -42,10 +41,16 @@ func main() {
 		},
 		Commands: []*cli.Command{
 			&cli.Command{
-				Name:   "pem",
+				Name:      "pem",
-				Action: fPEMCheck,
+				Usage:     "check if PEM certificate files expire too soon",
+				Action:    fPEMCheck,
+				ArgsUsage: "[PEM files...]",
 			},
 		},
+		Action: func(ctx context.Context, cmd *cli.Command) error {
+			cli.ShowAppHelpAndExit(cmd, 1)
+			return nil
+		},
 	}
 
 	if err := cmd.Run(context.Background(), os.Args); err != nil {