document schema for .tidyrc.json

[martyall]

Basically as a user I would like to know what all the options are and what they mean without having to run the cli tool for help. It would be nice to have either in the README, or potentially even better as comments in the generated .tridyrc file similar to stylish-haskell -- this would require changing to a yaml or dhall file since json doesn't support comments.

[natefaubion]

My intention is that that you use the CLI to generate the file. The tidyrc.json is meant to be a reproducible (as much as possible) snapshot of the arguments you used.