Correct sizings vor VMs for ICP V3.x needed in the doc

[AxelHoppe]

Since the VMs for V 3.x need much more power, the correct have to be added for V 3.x in the description.
Master and management nodes need at least 8 cores, that means m4.2xlarge sizing. Otherwise the placement of pods will fail

[jabbott7335]

As an FYK for the large sizing we are using the guidelines here https://github.com/ibm-cloud-architecture/refarch-privatecloud/blob/master/Sizing.md and specific filesystems ...