First of all, thank you for being interested in contributing to this project.
It's very easy to contribute. First, follow the instructions on the Setting up section of the README, but instead of just cloning the repository, fork it.
After you have made changes to the project and tested them, create a Pull Request explaining what are the changes you made, what new features were added and/or what bugs were fixed and one of the maintainers of the project will review your code and probably merge it.