code: func (s *Site) RegisterMediaTypes() {
  	for _, mt := range s.mediaTypesConfig {
  		for _, suffix := range mt.Suffixes {
  			_ = mime.AddExtensionType(mt.Delimiter+suffix, mt.Type()+"; charset=utf-8")
  		}
  	}
  }
docs: // RegisterMediaTypes will register the Site's media types in the mime
  // package, so it will behave correctly with Hugo's built-in server.