Fix config.md links

[Paragoumba]

Checklist

• Tests written for new code (and old code if feasible)
• Linter and other CI checks pass
• Sign-off given on the changes (see CONTRIBUTING.md)

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This change is marked as an internal change (Task), so will not be included in the changelog.

[richvdh]

Hi! Thanks for the contribution.

I'm afraid we don't accept contributions signed off under a pseudonym, per CONTRIBUTING.md, so we'll need your real name to be able to accept this.

If you prefer, you can provide this privately by emailing dco@matrix.org, though the contributing guide doesn't seem to mention this (#26654).

[CLAassistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.
_{You have signed the CLA already but the status is still pending? Let us recheck it.}