Well after going through the wiki, two thirds of the documentation in hpl2/Tools/editor/Level Editor/ just discuss how to use the level editor, what each of the left panes do (fog, static objects, lights, etc) and the basic navigation of such.
The other tutorials are basically just some small faqs which are also quite detailed, which can be found in hpl2/Level Editor/level_editor/ but one or two of them have error images as well, so a nice touch on them would probably be appropriate
Edit: Also, I do not mind assisting as well. I'm no expert of course, but I can teach how to make a simple map layout and stuff (floor, ceiling, 4 walls, door, decoration, window, lights, etc)