For a general readme, I think the best would be to just keep whatever the author chose to provide... but if it's more like an information file that's supposed to be displayed in a client or that contains complementary information for the car, then it probably would be best to use something like the carXXXX.cfg files I used in Simple Garage. As I said, Pretty Garage currently counts them among the car files, but does nothing with them. I did little to nothing with them even in Simple Garage, so I'm open to change their name and/or format, but I think the idea itself is useful. Dreadnaut mentioned something similar recently.