Update roi_methods.py
Update roi_methods.py

clarified inputs based on my understanding of the code. I think circles should more or less work for all cases but you might consider rectangles at some point too.
danforthcenter/plantcv,stiphyMT/plantcv,stiphyMT/plantcv,stiphyMT/plantcv,danforthcenter/plantcv,danforthcenter/plantcv