Github diffs PNG and SVG images I believe.
In general one should not use PSD in an open source project, because it requires costly proprietary software. Also does not run on Linux
There's a huge difference between displaying a simple, well documented open format and handling proprietary binary formats.
But there are plenty of libre software which are able to open a very large set of PSDs. Even if not everything was working perfectly, it would still be a good starting point.
https://github.com/makezonefablab/MakersBook01_MusicBox/comm...