init/Kconfig directs the user to Documentation/sched-rt-group.txt, but
the file is actually in Documentation/scheduler/sched-rt-group.txt.

This patch corrects the pathname mentioned in init/Kconfig.
Signed-off-by: NAdrian Knoth <adi@drcomp.erfurt.thur.de>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NIngo Molnar <mingo@elte.hu>