In general the contributing guidelines of OpenUI5 also apply to this project. They can be found here:
https://github.com/SAP/openui5/blob/master/CONTRIBUTING.md
Some parts might not be relevant for this project (e.g. the browser-specific requirements like jQuery, CSS and accessibility in the "Contribution Content Guidelines") and the contribution process is easier (pull requests will be merged directly on GitHub).