fix(chart:k8up): Fix outdated README

[mhutter]

Summary

• Short summary of what's included in the PR
• Give special note to breaking changes: List the exact changes or provide links to documentation.

Checklist

For Helm Chart changes

• [x] Categorize the PR by setting a good title and adding one of the labels: bug, enhancement, documentation, change, breaking, dependency as they show up in the changelog
• [x] PR contains the label area:chart
• [x] PR contains the chart label, e.g. chart:k8up
• [x] Commits are signed off
• [x] Variables are documented in the values.yaml using the format required by Helm-Docs.
• [ ] Chart Version bumped if immediate release after merging is planned
• [x] I have run make chart-docs
• [ ] Link this PR to related code release or other issues.