Some time ago, the Docs team decided to retire very old documentation from docs.fedoraproject.org,
see Time to retire the old Docs website.
You can still find that guide in the designated archival location:
https://pagure.io/fedora-docs-web/blob/master/f/public_html/en-US/Fedora_Draft_Documentation/0.1/html/RPM_Guide
The assumption was that the material is so old that its content is not useful anymore.
I am not sure that it holds for this particular guide — I have not looked at it.
Also, I am not sure if it makes sense to link to that Pagure repo from rpm.org,
since the repo is not (easily) viewable as HTML pages.