website: extend info on m5ops and tips for disk

On the m5ops page, this commit added a section about the "_addr" version
of m5ops and some examples of using m5ops.

On the disks page, this commit added a tips under the qemu method.

Change-Id: Ifb090a493fc5feee6edb0edc24a4b2a70015501e
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5-website/+/62371
Reviewed-by: Bobby Bruce <bbruce@ucdavis.edu>
Maintainer: Bobby Bruce <bbruce@ucdavis.edu>
Tested-by: Bobby Bruce <bbruce@ucdavis.edu>