Like most of my other asset packs these are public domain so nothing is required, there is no license or anything. Credit is always cool!! But mostly cuz i enjoy seeing whatever they get used in :)
I do wish you’d use the CC0 though. As this review of the CC0 explains, in jurisdictions not descended from the British legal system, saying “public domain” may not have any legal meaning.
The example they study is Germany, where there’s no legal mechanism for putting things into the public domain prematurely (the CC0 has an “if that’s not possible” fallback that provides equivalent permissions as a license) and you can’t pre-emptively give away rights that are written into law later (the CC0 solves that with a legally binding promise to not exercise those rights).