SuperCollider's documentation is in the .rtf format. .rtf files can be read with KWord, Abiword or OpenOffice.org. UnRTF can also prove to be useful.
There is also emacs-rtf, but it doesn't have a useful release yet.
You can access SC3's RTF Help and Tutorial files within emacs by typing C-c C-h and entering Help at the minibuffer prompt. From there simply select the topic you want to look at, then press the middle mouse button (or the left & right buttons simultaneously) on the selected item. AFAIK this doesn't require any special additions to emacs.
Another emacs amenity: Help subject completion! Just type in the first letters of a topic and press Enter. If more than one topic begins with those letters emacs will display the list of available items. Middle-click on an item to select and display its Help file.