This link, When to use Docker Official Images, says that These images have clear documentation. Where is it the documentation? For instance, for python image, I don’t see any documentation there.
It refers to the image description, which shows how to use the image.
The python image you picked has a description on how to create your own image using the python image as base image.
Other images like postgres will describe how to run the image as a container and explain the available environment variables and volumes (if existing).
The description will not include the documentation for the containerized application/service/programming language itself.