Document all hooks and how to use them

Did you verify this is a real problem by searching Stack Overflow and the other open issues in this repo?

Yes, the current hooks documentation does not describe all hooks and use-cases. Also the link in https://github.com/NativeScript/nativescript-cli/blob/master/README.md#extending-the-cli is broken.

Tell us about the problem

We need to document all hooks for CLI and how the plugins and users can get benefit of them.

Tasks:

• Fix the link in https://github.com/NativeScript/nativescript-cli/blob/master/README.md#extending-the-cli
• Document all hooks and when they are executed.
• Describe how to use the hooks and add examples.
• Add tests that verify the examples in the previous step work correctly and will not be broken in future release.

從 CLI README 的「Extending the CLI」章節及其中的失效連結開始。盤點各個 hook 及其執行點，然後記錄它們的用法，並為外掛程式和使用者提供範例。新增測試來執行文件中的範例，並確認它們仍能正常運作。