All of the instructions for contributing from the main repository apply, and won't be repeated here. You simply need to change references to homebrew/homebrew-cask (that repository) to homebrew/homebrew-cask-eid (this repository).
All Cask names and tokens should be of the form eid-<country-code>.
In addition, all Casks should have at least two standard name fields where only the country name changes:
name 'Electronic identity card software for <Country>'
name 'eID <Country>'If the software has another official name, it should be set above these.