See discussion for reference: #5684 (reply in thread)

Changes proposed in this pull request:

• Add clear steps for initial OIDC setup
• Remove post-installation steps since I figured it might be confusing when most of the focus is on the initial setup and doing it later will make it harder to keep administration access. If that is desired, I recommend making it more detailed.

How to test the feature manually:

1. Set up OIDC by following instructions
2. ???
3. Profit

Pull request checklist:

• clear commit messages
• code manually tested
• unit tests written (optional if too hard)
• documentation updated

Additional information can be found in the documentation.