A common source of confusion within tuned is the lack of suffix
on the readahead specification in the throughput-performance
tuned.conf. This confusion is resolved, in general, by comparing
the value, for example, to blockdev or lvdisplay output. Avoid
future end-user confusion by adding a comment to the
throughput-performance tuned.conf file, explaining that the default
is in KiB, and noting the allowance of a sector suffix as well.
Signed-off-by: John Pittman <jpittman@redhat.com>