notes added about pvl
notes added about pvl

thareUSGS/GDAL_scripts,USGS-Astrogeology/GDAL_scripts,USGS-Astrogeology/GDAL_scripts,USGS-Astrogeology/GDAL_scripts,thareUSGS/GDAL_scripts,thareUSGS/GDAL_scripts,USGS-Astrogeology/GDAL_scripts,thareUSGS/GDAL_scripts