Update README with host system requirements
Update README with host system requirements

Reported-by: Pridhiviraj Paidipeddi <fd8ea14509c256cbd04eaa4ee745a213945e70a1@linux.vnet.ibm.com>
Signed-off-by: Stewart Smith <ec31ab75ddf977353c8f660f92ea8b23f64aef25@linux.vnet.ibm.com>

open-power/op-test-framework,open-power/op-test-framework,open-power/op-test-framework