code: func (group *RouterGroup) StaticFS(relativePath string, fs http.FileSystem) IRoutes {
  	if strings.Contains(relativePath, ":") || strings.Contains(relativePath, "*") {
  		panic("URL parameters can not be used when serving a static folder")
  	}
  	handler := group.createStaticHandler(relativePath, fs)
  	urlPattern := path.Join(relativePath, "/*filepath")
  
  	// Register GET and HEAD handlers
  	group.GET(urlPattern, handler)
  	group.HEAD(urlPattern, handler)
  	return group.returnObj()
  }
docs: // StaticFS works just like `Static()` but a custom `http.FileSystem` can be used instead.
  // Gin by default user: gin.Dir()