Possible to add some documentation to a channel entry form?

Some of our channel entry forms are either a little on the complex side or it’s easy forget just how you style things (we have a LOT of styles) if you haven’t used it for a while. I’d love to be able to just have a simple block of documentation at the top of the entry form reminding editors how to style things, how to relate entries, etc. Is there currently a way to do this, either through native methods or an add-on?