#16 User manual - Mac OS X instructions
The user manual (http://arcem.sourceforge.net/manual/arcem-1.50.html) lists the Mac OS X sections as "TODO", while some of the "Unix / Linux" blocks have text. As OS X is a BSD variant the instructions are essentially identical so why not drop all but one of the Mac OS X place holders and label the others as "Unix / Linux / Mac OS X"
You'll still need one specific Mac OS X block in the System Requirements, indicating that you'll need a set of X11 libraries installed, either Apple's own bundled libraries or from the Xquartz site, if your Running Mountain Lion 10.8 (See: http://en.wikipedia.org/wiki/X11.app\).
You may also want to add a few words on the requirement for a full keyboard (numeric key pad) and a mouse. As you won't get very far with the laptop keyboard and Trackpad, I'm guessing in any of the OS'es .
The intention was/is to (re) create a "proper" OSX port. I did a chunk of it, but then other things got in the way. This suggestion seems fine to me anyway. FWIW there is no real requirement for a numeric keypad (I hate the damn things, so this is a pet issue for me).