Added a note about the recommended version of RHEL for block storage in section 3.2 of 3.10 Operations Guide. Note: The recommended Red Hat Enterprise Linux (RHEL) version for block storage is RHEL-7.5.3. Link to verify: https://access.qa.redhat.com/documentation/en-us/red_hat_openshift_container_storage/3.10/html-single/operations_guide/#Block_Storage