Contributings are always welcome, nothing specific. Since there are no unit or e2e tests, you need to provide a link to working example of a bugfix or a feature. You can use gh-pages branch when you make pull request.
Prerequirements: NodeJS 7+, NPM 4+.
Install needed deps via npm install (it also compiles browser version of UglifyJS).
To run development server you need to run npm run develop and open http://localhost:8100.
To compile the app (without dev server stuff) run npm run bundle.