Better documentation for router getScreenOptions

The documentation of getScreenOptions needs some clarification:

• the headline is getScreenOptions(navigation, screenProps) but the text explains 3 parameters. What is about navigationOptions?
• The text says "retrieve the navigation options for a screen". Why the function is named screen options while it returns navigation options?
• The example code uses addNavigationHelpers which does not exits anymore?
• For me is not clear where I can use this function, p.ex. in screen, in my custom router, etc. Please improve the example to make this more clear.

从链接的 custom-routers 文档中的 getScreenOptions 部分开始，检查其签名、说明以及使用 addNavigationHelpers 的示例。明确参数、术语、当前 API 的用法以及该函数的使用位置；当示例和周围文本能够回答每一点，且不依赖过时的 API 时，即表示完成。