We're run into similar problem. We've created our own documentation prior to distribution of information to email users. That doesn't guarantee they understand or comply with the update request and we have to regularly do individual reminders.
The only place I know where Update your Progress email is described is https://success.clarizen.com/hc/en-us/articles/205712428-Email-Notifications-#Progress - and it is not precisely "email user oriented".
If Clarizen doesn't intend to maintain a dedicated email user instruction page, it could maybe offer us to customize the body of the email - where we could add a link to our ad'hoc documentation/manual.
Thank for considering this point.