Include docs on creating github app for example

Would it be possible to add code above the “example” section of the docs, or in a readme in that directory, that walks through the right github app settings for running the example?

As a first-time user of this library, I went to try the example. Running the example server was super straightforward, but I was left to guess at what options to set when creating my github app. Specifically, I had to infer what permissions to ask for, given the description of what the app would do, and I had to search in the code to find what “DefaultWebhookRoute” referred to.

Start with the documentation around the “example” section and the example directory's README, then inspect the example and the DefaultWebhookRoute reference mentioned in the issue. Document the GitHub App settings, required permissions, and webhook route so a first-time user can run the example without searching the code.