Add project documentation to the README
There are nice instructions in the README for running the project, but they're somewhat generic to similar node.js apps. (In fact, I'm not even sure I understand why it couldn't be a simple client-side webpage, but that's another issue.)
It would be great to have some brief overview of how the project actually works (i.e. "implementation notes"), for example listing which files are the main ones and what their content and purpose is.
The ideal, IMO, would be something similar to this README, but any small steps in that direction would already be quite helpful to help others know where and how to contribute. I'd say the bare minimum should be a one-sentence description of what the project is/does, and a link to the live demo. Anything beyond that would be welcome additions, of course.