Thank you for your interest in Minecraftly. Contributing to Minecraftly is easy, just fork the project on GitHub, make your changes and submit a pull request to get your code merged. That's all there is to it.
Check out GETTING-STARTED.md for more information about setting up the development environment for Minecraftly, finding issues to work on, etc...
If you are new to open source and/or GitHub, or just aren't sure about some details in the contribution process, here's a tutorial to get you started: How to Contribute to an Open Source Project on GitHub