feat: permissions (#168)

- Load `app-permissions` from schema exported by `@octokit/openapi`
- Update documentation in README.md
- Implement the `permissions_*` inputs in the action code

---------

Co-authored-by: Parker Brown <17183625+parkerbxyz@users.noreply.github.com>

tests/README.md

@@ -17,3 +17,14 @@ or with npm
 ```
 npm test
 ```
+
+## How the tests work
+
+The output from the tests is captured into a snapshot ([tests/snapshots/index.js.md](snapshots/index.js.md)). It includes all requests sent by our scripts to verify it's working correctly and to prevent regressions.
+
+## How to add a new test
+
+We have tests both for the `main.js` and `post.js` scripts.
+
+- If you do not expect an error, take [main-token-permissions-set.test.js](tests/main-token-permissions-set.test.js) as a starting point.
+- If your test has an expected error, take [main-missing-app-id.test.js](tests/main-missing-app-id.test.js) as a starting point.