middleware helmet changes.

router check and panic message change.
README enhancement

example/main.go

@@ -12,8 +12,22 @@ func main() {
 	// create a new router
 	r := mux.NewRouter()
 	r.Use(middleware.CORS(middleware.CORSOption{
-		AllowedOrigins: []string{"*"},
-		MaxAge:         60,
+		AllowedOrigins:   []string{"*"},
+		AllowedMethods:   []string{"GET", "POST", "PUT", "DELETE", "OPTIONS"},
+		AllowedHeaders:   []string{"Accept", "Authorization", "Content-Type", "X-CSRF-AccessToken", "X-Real-IP"},
+		ExposedHeaders:   []string{"Link"},
+		AllowCredentials: true,
+		MaxAge:           300,
+	}))
+
+	r.Use(middleware.Helmet(middleware.HelmetOption{
+		StrictTransportSecurity: &middleware.TransportSecurity{
+			MaxAge:            31536000,
+			IncludeSubDomains: true,
+			Preload:           true,
+		},
+		XssProtection: true,
+		XFrameOption:  middleware.XFrameDeny,
 	}))
 
 	// you can use any middleware that is: "func(http.Handler) http.Handler"