It'd help if you gave us the file(the whole thing, not just the png).
It's simple though. Folder named Print_RATIO_NAME
description.txt that says anything.
Blank server.cs file.
icons and prints folders.
png file in each folder with the same name, icon size one in icons folder, regular size one in prints folder.
HERE's an ancient guide on making prints too. Basically says the same thing though.