Document that server-side apply is necessary for the CRDs

Summary

Because the CRDs have grown quite a bit, it's now necessary to apply then with the server side flag.

[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.