Document the interactions between loglevel and the sysrq output.  Also
document how to work round it should output be required on the console.
Signed-off-by: NAndy Whitcroft <apw@canonical.com>
Cc: Martin Mares <mj@ucw.cz>
Cc: Randy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>