update README with test suite names and purpose
update README with test suite names and purpose

Suggested-by: pridhiviraj <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