Contributors to cellfinder are absolutely encouraged, whether you want to fix bugs, or add new features to better suit your data.
If you would like to contribute to cellfinder (or any of the upstream tools like amap, neuro, brainio, imlib etc.) please get in touch via email, or better yet by starting a discussion on the gitter dev channel. You might find that there is someone already working on something similar, and you can work together.
If you're not sure where to start, check out the issues (and the issues of the other repositories).
For a more practical guide on how to contribute, such as setting up a development environment, please see here.