feat: better flags

cmd/invoicer/main.go

@@ -1,20 +1,25 @@
 package main
 
 import (
-	"fmt"
+	"flag"
 	"os"
 )
 
 func main() {
+	for n, c := range commands {
+		c.Register(n)
+	}
 	if len(os.Args) < 2 {
+		flag.PrintDefaults()
 		return
 	}
 
 	for n, c := range commands {
 		if os.Args[1] == n {
-			c.Run()
-			break
+			c.Run(n)
+			return
 		}
 	}
-	fmt.Println("cmd not found")
+
+	flag.PrintDefaults()
 }