The documentation has been updated and the latest documentation is available here
Deployment instructions for the upgrade:
The XML Documentation 4.0 upgrade package is available here. Please refer this for the list of detailed upgrade instructions. These are also available in the latest installation guide shared above.
Please note that you need to be on the 3.8.5 version or higher to be able to upgrade to 4.0. If you have an older version of XML Documentation deployed, please first upgrade to 3.8.5 and then to 4.0 using the attached upgrade process.