text: Title: Fix the Errors/Warnings  when building Qlib's documentation.
  Body: ## 📖 Documentation
  
  <!-- Please specify whether it's tutorial part or API reference part, and describe it.-->
  ![image](https://user-images.githubusercontent.com/465606/200975890-76ab0559-bd44-466d-af7b-8ffe71b6d1a9.png)
  