Show usage when incorrect wsdl is not set, added comments

cli.go

@@ -10,6 +10,7 @@ import (
 	"go/format"
 	"log"
 	"os"
+	"fmt"
 
 	gen "github.com/sanbornm/gowsdl/generator"
 )
@@ -20,33 +21,43 @@ var vers = flag.Bool("v", false, "Shows gowsdl version")
 var pkg = flag.String("p", "myservice", "Package under which code will be generated")
 var outFile = flag.String("o", "myservice.go", "File where the generated code will be saved")
 
+
 func init() {
 	log.SetFlags(0)
 	log.SetOutput(os.Stdout)
 	log.SetPrefix("🍀  ")
 }
 
 func main() {
+	flag.Usage = func() {
+	    fmt.Fprintf(os.Stderr, "Usage: %s [options] myservice.wsdl\n", os.Args[0])
+	    flag.PrintDefaults()
+	}
+
 	flag.Parse()
 
+	// Show app version
 	if *vers {
 		log.Println(version)
 		os.Exit(0)
 	}
 
 	if len(os.Args) < 2 {
-		log.Fatalln("WSDL file is required to start the party")
+		flag.Usage()
+		os.Exit(0)
 	}
 
 	if *outFile == os.Args[1] {
 		log.Fatalln("Output file cannot be the same WSDL file")
 	}
 
+	// load wsdl
 	gowsdl, err := gen.NewGoWsdl(os.Args[1], *pkg, false)
 	if err != nil {
 		log.Fatalln(err)
 	}
 
+	// generate code
 	gocode, err := gowsdl.Start()
 	if err != nil {
 		log.Fatalln(err)
@@ -66,6 +77,7 @@ func main() {
 	data.Write(gocode["types"])
 	data.Write(gocode["operations"])
 
+	// go fmt the generated code
 	source, err := format.Source(data.Bytes())
 	if err != nil {
 		fd.Write(data.Bytes())