Make it very explicit that this is a demo, and that customers will have to deploy this, keep up-to-date with any changes you publish, and also maintain their own infrastructure and Stripe accounts – i.e. clarify that this is not a managed service.
The readme.md doc should serve as an introduction and table-of-content that links to relevant docs. At the moment it feels like it jumps straight into the details and I had a hard time understanding the big picture. I know there’s some of this in the API Subscription doc but I think a high-level overview in the readme would be worthwhile.