chore: add Github example

[frixaco]

Checklist

• [x] run npm run test and npm run benchmark
• [ ] tests and/or benchmarks are included
• [ ] documentation is changed or added
• [x] commit message and code follows the Developer's Certification of Origin and the Code of conduct

Thank you for the library! I didn't find any Github OAuth example and thought this might be a good chance to contribute to library that I'm using. So I added one. Let me know if this is needed or if you have any type of feedback!

Waiting for #174 to be answered.

[mcollina]

I'm not sure you'd get an answer for #174. If you'd like to send a PR for that it would be awesome.

[frixaco]

@mcollina oh ok, so it's like a bug or something? I could do a PR for that and then remove the comment from this PR for updating refresh_token

[mcollina]

oh ok, so it's like a bug or something?

I have no real clue, you have likely more experience than me using this module with GitHub ;).