basicly you follow the windows gtkradiant 1.5 instalation (ive only got it working for 1.5)
make sure you edit the correct path in the trem.game file
enginepath_win32="c:/Program Files/Tremulous/" -this doesnt matter
enginepath_linux="/usr/local/games/tremulous/" -neither does this
enginepath_macos="" -insert path to folder containing tremulous.app here in quotation marks
dont put in my comments
right- or control- click on the gtkradiant15 app and choose "show package contents"
go contents -> resources -> sw -> radiant15 --this is where the trem.game FOLDER goes, as well as the games folder with the trem.game FILE inside
as far as i remember, everything else is exactly the same
oh, i dont know if it compiles maps correctly though, just thought id let you know
all the necesary files can be gotten
here