Improve environment variable usage documentation

## Describe the error

I have completely read the Chinese installation document of Answer. I need to add a more complete description of the `AUTO_INSTALL` setting in `environment variables`. If there is no docker volumes mapping, when using environment variables for Answer installation, delete the Answer to run the container. And run the Answer container again, Answer will populate the database again, but the database already has content, Answer will prompt an error (the config.yaml file is missing, and the database uses postgresql).

### Reappear

Set AUTO_INSTALL to true according to the document, and the installation will be automatically successful. The data has been written to the database. At this time, Answer can be accessed normally. After deleting the running container and using the same parameters, Answer will write the configuration to the database again. information, but the same configuration information already exists in postgresql.

### Expected behavior

AnswerYou can use environment variables for parameter configuration and run, no configuration file is required.