Add using GitHub app authentication in README

[Tatsumi0000]

Behavior

Before the change?

• There was no explanation in the README for authentication using GitHub App.

After the change?

• Add using GitHub app authentication for README.

Other information

Reference information.

• Authenticating with GitHub Apps

---

Additional info

Pull request checklist

• Tests for the changes have been added (for bug fixes / features)
• Docs have been reviewed and added / updated if needed (for bug fixes / features)
• Added the appropriate label for the given change

Does this introduce a breaking change?

Please see our docs on breaking changes to help!

• Yes (Please add the Type: Breaking change label)
• No

Pull request type

Please add the corresponding label for change this PR introduces:

• Bugfix: Type: Bug
• Feature/model/API additions: Type: Feature
• Updates to docs or samples: Type: Documentation
• Dependencies/code cleanup: Type: Maintenance

---

[kfcampbell]

Thank you for contributing! Builds are failing due to an unrelated issue I need to sort out. When I do, this PR will be merged!

[Tatsumi0000]

Thank you for contributing! Builds are failing due to an unrelated issue I need to sort out. When I do, this PR will be merged!

Thanks for review it!
I understand the merge.