add note about friesen ammonia calculations
add note about friesen ammonia calculations

allisony/pyspeckit,dinossimpson/pyspeckit,low-sky/pyspeckit,pyspeckit/pyspeckit,mikelum/pyspeckit,dinossimpson/pyspeckit,vlas-sokolov/pyspeckit,keflavich/pyspeckit,mikelum/pyspeckit,bsipocz/pyspeckit,bsipocz/pyspeckit,e-koch/pyspeckit,jpinedaf/pyspeckit,pyspeckit/pyspeckit,allisony/pyspeckit,low-sky/pyspeckit,jpinedaf/pyspeckit,keflavich/pyspeckit,vlas-sokolov/pyspeckit,e-koch/pyspeckit