The system documentation is currently rewritten in a new system that builds HTML from ReStructuredText/Sphinx sources.
The git-Repository is at https://git.cacert.org/cacert-infradocs.git/
The generated documentation is published to https://infradocs.cacert.org/.
Instructions on how to work on the new documentation are available at https://infradocs.cacert.org/building.html.
For some more background information see the mailing list thread at https://lists.cacert.org/wws/arc/cacert-sysadm/2016-05/msg00000.html.