I haven’t tried on Windows but I just tried on Mac and “it just worked” ™. I installed via LuaRocks to a user local installation and ran with ldoc path/to/lua/files and got the output in the “doc” folder.
I followed Windows instructions they gave, tried many variations with ldoc and all of the options it gives with -h same deal. Tried going to folder with config.ld and ldoc . doesn’t work either.