Adding extra markup to wp editor

I am working on a plugin which adds a custom post type. It would be very helpful if there was a way to add some extra markup to clarify what the editor is supposed to be use for.

So, I haven’t found any good filters for it (closest I find is the_editor, which is far after the wp-editor-wrap where I would want it). Any suggestions on where to look, or am I better off looking at using javascript for it?