Add actual reference(yardstick) values for IOPS
What does this MR do?
Changed the documentation to be more clear about what storage parameters should be in regards to IOPS, as most customers thought that the value given in the example (for mechanical disks) is some sort of reference, when in fact it isn't as that is a value that is way under what we consider acceptable (read 8,000 iops; write 2,000 iops).