docs: fix broken link in rook README

[anders-elastisys]

What kind of PR is this?

Required: Mark one of the following that is applicable:

• [ ] kind/feature
• [ ] kind/improvement
• [ ] kind/deprecation
• [x] kind/documentation
• [ ] kind/clean-up
• [ ] kind/bug
• [ ] kind/other

Optional: Mark one or more of the following that are applicable:

[!important] Critical security fixes should be marked with kind/security Breaking changes should be marked kind/admin-change or kind/dev-change depending on type

• [ ] kind/admin-change
• [ ] kind/dev-change
• [ ] kind/security
• [ ] [kind/adr]()

What does this PR do / why do we need this PR?

...

• Fixes #

Additional information to reviewers

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Checklist

• [ ] Proper commit message prefix on all commits
• Change checks:
  • [ ] The change is transparent
  • [ ] The change is disruptive
  • [ ] The change requires no migration steps
  • [ ] The change requires migration steps
• Metrics checks:
  • [ ] The metrics are still exposed and present in Grafana after the change
  • [ ] The metrics names didn't change (Grafana dashboards and Prometheus alerts are not affected)
  • [ ] The metrics names did change (Grafana dashboards and Prometheus alerts were fixed)
• Logs checks:
  • [ ] The logs do not show any errors after the change
• Network Policy checks:
  • [ ] Any changed pod is covered by Network Policies
  • [ ] The change does not cause any dropped packages in the NetworkPolicy Dashboard
• Pod Security Policy checks:
  • [ ] Any changed pod is covered by Pod Security Admission
  • [ ] Any changed pod is covered by Gatekeeper Pod Security Policies
  • [ ] The change does not cause any pods to be blocked by Pod Security Admission or Policies
• Falco checks:
  • [ ] The change does not cause any alerts to be generated by Falco