Website: https://stripefees.com
Access the latest compiled version at https://stripefees.com/fees.json
The PHP classes exist purely to give some structure. Open the /src/fees/_template.php file, add the fee structures (see existing files for examples), save it as {ISO COUNTRY CODE}.php in the same directory, run /src/generator.php to build the new fees.json, then issue a pull request.
Edit the relevant {ISO COUNTRY CODE}.php file in /src/fees/, run /src/generator.php to build the new fees.json, then issue a pull request.