希望添加 Contribute 指南

[liuweiGL]

试用下来发现很多功能不支持，想看看能不能自己实现。

[atorber]

@liuweiGL We are glad you're interested in the XP project. If you want to contribute code：

1. To wehaty's official website to learn about wehcaty's API first https://wechaty.js.org/docs/api/
2. Then check the source code of XP, understand the architecture logic and try to add your code

We look forward to your contribution.