Error: Middleware "strapi::session": App keys are required

Hi @Eventyret thank you for your feedback.
I think it would be quite common for more than one developer to be working on a strapi project. Suppose I created my strapi project with no problems, and I push the repo to github. Then developer-2 clones the repo and wants to start working on it.

What steps should developer-2 take to run strapi?