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.

CLI README の「Extending the CLI」セクションと、その壊れたリンクから始めます。フックとその実行ポイントを洗い出し、続いてプラグインとユーザー向けにその使用方法と例をドキュメント化します。ドキュメント化した例を実行し、それらが引き続き動作することを確認するテストを追加します。