Prior to NAV 5.0 end-user companies could add their own notes and instructions to any help topic by means of the Company Notes feature. I recall I was happily using it when writing the Help for the Dutch localization as part of the 4.0 project back in 2004. If my memory doesn't fail there were some security issues around that led to the deprecation of it in NAV 5.0.
Now with NAV 2013 there finally is a successor to Company Notes: OneNote. Running NAV 2013 you probably have noticed the grayed out OneNote icon and like many didn't pay much more attention to it after that. But I think it's a cute successor to company notes or at least - but I actually should say more than - worthwhile to consider it the successor. Of course it does not integrate so nicely with the standard help system, but if gives you various other options that come with OneNote like DTP features and much more.
You can document your notes and instructions at page or at record level and store the OneNote notebook locally or on a share. You can associate separate notebooks with each (role center) profile thus differentiating instructions for the same page.
Details on how to enable OneNote has been described in various other post listed below, so no need for me to redo that job.