Yes, when you create a new request type or edit a request type, the is a field for notes that you can put in a link. You can also put documentation in faq but i thing the best solution is messages which will appear on the home screen. Create a new message as below and select who it is applicable to. Public is the one that shows on the home screen.
As far as i can remember, the public one is the exception and appears before login.
We have accomplished this by adding instructional information to the Welcome Message:
This appears for all users prior to log-in on the actual log in page.
The Login Message can be configured via Settings > General > Authentication > Login Message.
This field accepts bbCode formatting, so you can change the size, type, and color of text while also including images, quotes, and links.
I hope this helps! Please let me know if you have any questions or concerns about this recommendation.