The guide was moved to the Bitcoin Core documentation repository.
It now includes not only instructions to run on a debian host, but also on any recent fedora host.
This is an ongoing effort to reduce the fraction caused by incoming pull requests to docs (usually fixups, typo fixes, version bumps).
This is especially important for documentation that is independent of any release cycles and should thus be up-to-date regardless of a tag on a non-master branch.
Finally, fetching a shallow copy of the source is less heavy, as many binary png files are moved out of the repo.