文档亟待丰富

- [ ] I have searched the [issues](https://github.com/antvis/f2/issues) of this repository and believe that this is not a duplicate.

### What problem does this feature solve?
目前的文档对新手使用很不友好，无法准确快速的上手

### What does the proposed API look like?
详细的介绍每个api的使用方式以及对应的demo

No files, tests, or entry points are named. Review the repository's current documentation and public API list first, then define the API and demo coverage needed for newcomers and verify that each documented API has a usable example.

Written by the indexing model from the issue text.