### Motivation
When writing Pulsar docs, we can adopt a consistent writing styles, whoever the author is.
Here I introduce [Google Developer Documentation Style Guide](https://developers.google.com/style/) for Pulsar technical docs. The style guide generally conforms to with most popular technical writing styles, such as *IBM style guides*, *Microsoft style guide*, *The Chicago Manual of Style*, and so on.
In addition, *Google Developer Documentation Style Guide* is open to all, and the link is easy to share among all participants.

### Modifications
1. Restructure the content of the site2/reademe file: website, doc, and translation.
2. Introduce *Google Developer Documentation Style Guide* in **Contribute to documentation**.