helm-charts/charts/ceph/README.md

Creating this as a separate directory, rather than defining directly in `app-of-apps/templates/apps.yaml`, because this method allows the creation of a separate `values.yaml` (which I've adapted from [here](https://github.com/rook/rook/blob/cb44c7b88fb346f3b120e8bda769ac808ec60880/deploy/examples/cluster-on-pvc.yaml) based on advice [here](https://rook.io/docs/rook/latest/Helm-Charts/ceph-cluster-chart/#ceph-cluster-spec))