adding initial version of 'keywords from location' script

adds keywords based on GPS coordinates of a photo (lat and long GPS EXIF tags)
depends on JSONHelper application and calls Google Geocoding API for reverse geocoding lat and long
renaming importImages parameter to imageSel

for easier modification to make it runnable as a service
updating readme with information on the new 'Keywords From Location' script

adding additional information on how to install script as a Mac OS X service