Multiple folders support

[jaredcat]

I wanted to set this up in docker, but have it run against multiple folders. Looking at the examples, it looks like you can only do one folder at a time? Or can I do something like: --volume /path/to/first-folder:/work/images/first --volume /path/to/second-folder:/work/images/second since the script supports subdirectories?

If so, might want to update the readme to show off this functionality