A little helper for all of you that have more than one Info.plist file...
find . -name Info.plist | xargs -I {} /usr/libexec/PlistBuddy -c 'Add NSLocationWhenInUseUsageDescription string' {}
It will add the needed tag to all of the Info.plist files in the current directory (and subfolders).
Another is:
find . -name Info.plist | xargs -I {} /usr/libexec/PlistBuddy -c 'Set NSLocationWhenInUseUsageDescription $YOURDESCRIPTION' {}
It will add your description to all files.