Don't forget to put it under an open source license! Otherwise it's just source available, not open source. I think you also need permission from anyone else involved in order to do that, just did some research and the Creative Commons License is probably what you want it under, specifically the CC BY-NC-SA, BY stands for Attribution, basically "Credit me". NC stands for noncommercial, so "Don't sell it", and SA stands for Share-Alike, or "put yours under the same license if you use mine". If you Don't pick a license it's considered all rights reserved according to the websites I looked at. Just remember you don't need to choose immediately, you can just make the license change as a commit whenever. Last thing make sure you specify if you don't own something or want something NOT under the license and what the rights are for it, like if you want an image open but not the character, luckily you can just slap that on the start of the readme as a disclaimer. Good game btw. If you need more info on this license check Wikipedia or something idk.