This is the source of the Cargo Contributor Guide, published at https://rust-lang.github.io/cargo/contrib/. It is written in Markdown, using the mdbook tool to convert to HTML. If you are editing these pages, the best option to view the results is to run mdbook serve, which will start a web server on localhost that you can visit to view the book, and it will automatically reload each time you edit a page.
This is published via GitHub Actions to GitHub Pages.