They wrote

Feel free to fork the project under a

(yes, the sentence ends with the 'a')

The ZUDoom GitHub project description says

UZDoom is a feature centric port for all Doom engine games, based on ZDoom, adding an advanced renderer, powerful scripting capabilities, and forked under a

It ending with 'forked under a' is probably a reference to that comment? lol, nice reference joke, but I hope they change it after a while, because as a description it's quite confusing.