make github app that posts images of diff on pull requests

Resources I've found so far.
Offical Github tutorial, although it uses ruby
https://docs.github.com/en/developers/apps/setting-up-your-development-environment-to-create-a-github-app

here's a medium post using node
https://medium.com/@knidarkness/creating-a-github-app-with-node-js-3bda731d45b9
One thing interesting about that is there's on official github npm package for thing stuff `@octokit/app`

General info about apps
https://docs.github.com/en/developers/apps