You are very wrongfully assuming that anyone even cares. 
Just do it, man. Make a common library, put it up publicly with a short note on what it does and how – don’t need to be detailed. Nobody guarantees any future readers they’ll find anything of use. The amount of abandoned projects out there is gigantic. Just don’t think about it and do it how it’s easiest on you. If that means a public repo, so be it.