I know the code is in here: https://github.com/facebook/react-native-website
and it uses Docusaurus, but, the markdown is automatically generated from the code or it was all written manually?
And if it's automatically generated, what is being used?
The docs are written manually using markdown. Docusaurus takes that markdown and generates the HTML/JS which is published.
The markdown is available in the repo in the docs folder.