Describe the bug

The quickstart guide's "Configure Provider" section doesn't mention that GitHub Copilot uses a different authentication flow than other providers. Readers selecting GitHub Copilot may be confused when no API key is requested.

To Reproduce
Steps to reproduce the behavior:

1. Follow the Quickstart guide at https://block.github.io/goose/docs/quickstart#configure-provider
2. Run goose configure and select GitHub Copilot as your provider
3. Notice the authentication flow differs from what the docs describe

Expected behavior
An info or tip block in the Quickstart explaining that GitHub Copilot provider uses an auth code flow instead of an API key.

Screenshots

Please provide the following information

• OS & Arch: Kubuntu 25.10
• Interface: CLI
• Version: v1.19.1
• Extensions enabled: computercontroller, todo, skills, extensionmanager, developer, code_execution, chatrecall
• Provider & Model: GitHub Copilot – gpt-4.1