Documentation: update gluetun documentation link

[retrodaredevil]

Fixed link to control server documentation

Proposed change

This fixes a link to point to the new gluetun wiki documentation

Type of change

• New service widget
• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Documentation only
• Other (please explain)

Checklist:

• If adding a service widget or a change that requires it, I have added corresponding documentation changes.
• If adding a new widget I have reviewed the guidelines.
• If applicable, I have checked that all tests pass with e.g. pnpm lint.
• If applicable, I have tested my code for new features & regressions on both mobile & desktop devices, using the latest version of major browsers.

[github-actions]

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