docs: Optimize document formatting and content in document sites

[YuLuo]

Description:

Now that we have the documentation site.
so, we need to optimize document formatting and content in document sites.

We can refer this docs guide: https://github.com/ruanyf/document-style-guide.
in addition, we can install markdownlint plugin in vscode to check md style.

If this problem occurs, it means we need to change the formatting.