On root.cern.ch/drupal/content/users-guide there’s the statement:
“We will appreciate your comments on this edition. If you would like to contribute to a chapter, section, or even a paragraph, do not hesitate to contact us and send your comments to: rootdoc@root.cern.ch. You can also post your comments or questions in the section Documentation of the ROOT Forum.”
The two links are broken and sending an email is not possible: