@dualhammers I humbly submit that all software that's going to have people using it other than the developer needs sales. Sales is about communicating the value of what you've built, and getting paid money is just one of the possible side effects of that process. Writing a good README is sales. Posting about your thought/build process on Masto is sales. Inspiring people is also sales.
@gosha I think all of those things are psychology to be sure, but I'd argue the way money and economic transactions have dominated interactions in our lives has caused a categorization inversion.
Writing a good README is writing, understanding what to write to communicate your goal is understanding people, which is psychology. :)