What files from `.openzeppelin` directory should be in version control (and which should be in `.gitignore`?

@gitpusha asked on Telegram:

is the .openzeppelin folder something I should put into my .gitignore

The OpenZeppelin SDK documentation covers the configuration files and which should be in version control, and which should be added to .gitignore:
https://docs.openzeppelin.com/sdk/2.5/configuration#configuration-files-in-version-control