Disclaimer! Pebble has been acquired by Fitbit at the end of 2016. Even though there are attempts in the community to recreate Pebble services, it currently seems that Pebble will be a dying platform. All Pebble services are still running but they may be terminated without any further notice. Take this into account before making any contributions to this project.
Easiest way to contribute is to clone this project and open the folder in CloudPebble. CloudPebble is an excellent web based Pebble development environment which lets you to skip setting up development environment. It also offers emulators of all current Pebble models to test your application. After making the changes you want create a pull request to this repository.
If you are feeling adventurous, you can set up real Pebble development environment by following the official guide. We recommend using any Unix based operating system.