Actually - when you take a deep breathe and plunge in, its not too bad. The steps here (
https://github.com/pharo-project/pharo/wiki/Contribute-a-fix-to-Pharo) are pretty good, the only caveat is you need to use a Pharo 8.0 image (not 7 like it says), as this makes it easier. I actually quite like the flow in Github for this kind of project, you can really see what is going on and also it gives you more widely applicable skills to boot. Highly encouraged.