1. No config. It really doesn't exist. But there is a config template, which is nearby:
lib/Crop/Config.ex.pm
but you have to go to dir and look around. There is also something about it in install/README. But you also have to find it and open it.
2. XML config. All config templates are in install/conf/. And their format is quite simple and obvious.
3. The phrase about "ease of writing scripts" actually has a foundation, but you perceive it as another empty advertising slogan.