Hi @Patrick_Werner,
you can find it here: https://docs.spring.io/spring-boot/docs/current/reference/html/boot-features-developing-web-applications.html#boot-features-spring-mvc-static-content.
Feel free to add a pull request to the camunda docs. The github pages are easily available by the cat icon on the top of the page. After editing on github, you can commit a branch, which may be pulled to master branch.
Cheers, Ingo