Scaling storage guide: local storage - missing guide how to add disks for LocalVolume sets

In the procedure for expanding the capacity with LSO, in the step 3iii the Storage class is assumed to have added disks or a new storage class is to be selected. The first option doesn't provide additional capacity (0B / X replicas) for the existing StorageClass and no other StorageClass (beside the default one) is available (e.g. on RHV based OCP cluster). 
There should be a procedure how to get more capacity to a StorageClass based on a LocalVolume Set or the need and creation procedure for another StorageClass based on a new LocalVolume Set should be explained as a prerequisite to be able to add additional capacity in this step.

Reported by: matthiasmuench

https://access.redhat.com/documentation/en-us/red_hat_openshift_data_foundation/4.9/html/scaling_storage/scaling-up-storage-capacity_rhodf#annotations:a4f6c670-b627-40cf-8ce8-5391ee308b01