We are always happy to see people interested in our work. Therefore if you have found a missing feature or a bug, you can either open a pull request, or an issue. As we have a Gitter channel, you can also join us
If you have installed clang, please run the script format-code.sh, located at the repo's root, before you commit. That would avoid a commit more, but it is not necessary.
An issue is a good start to contribute. If you have an idea for an extra feature, detail it as far as you can. Do not forget to add images that could help us seeing what you think.
A pull request is for us easier than an issue, as we do not have to code the feature ourself. Nonetheless do not forget to test your code before submitting it, or specify it in the comments.