updated data_prep.py to clarify where to edit
updated data_prep.py to clarify where to edit

jmolina116/kaldi-yesno-tutorial,jmolina116/kaldi-yesno-tutorial,jmolina116/kaldi-yesno-tutorial,jmolina116/kaldi-yesno-tutorial,keighrim/kaldi-yesno-tutorial,keighrim/kaldi-yesno-tutorial,keighrim/kaldi-yesno-tutorial