Update redhat-common elements README from free text to table formatting
Update redhat-common elements README from free text to table formatting

Change-Id: Ie87cf9937a54110719814046c4f46829e307ff3d

takahashinobuyuki/diskimage-builder,openstack/diskimage-builder,CSC-IT-Center-for-Science/diskimage-builder,switch-ch/diskimage-builder,CSC-IT-Center-for-Science/diskimage-builder,zioproto/diskimage-builder,switch-ch/diskimage-builder,zioproto/diskimage-builder,takahashinobuyuki/diskimage-builder,openstack/diskimage-builder