[doc] Add a Chinese version documentation & Fix a bug while building website locally.

[marcuswang6]

What is the purpose of the change

Add a Chinese version documentation for Flink ML

Brief change log

• Add a Chinese version documentation
• Fix a bug while building website locally

Does this pull request potentially affect one of the following parts:

• Dependencies (does it add or upgrade a dependency): (no)
• The public API, i.e., is any changed class annotated with @Public(Evolving): (no)

Documentation

• Does this pull request introduce a new feature? (no)