doc: document the relax_domain_level kernel boot argument

Document the kernel boot parameter: relax_domain_level=.

Signed-off-by: Paul Jackson <pj@sgi.com>
Cc: Michael Kerrisk <mtk.manpages@googlemail.com>
Reviewed-by: Li Zefan <lizf@cn.fujitsu.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/Documentation/cpusets.txt b/Documentation/cpusets.txt
index 894b844..1f5a924 100644
--- a/Documentation/cpusets.txt
+++ b/Documentation/cpusets.txt
@@ -546,6 +546,9 @@
  ( 4  : search nodes in a chunk of node [on NUMA system] )
  ( 5  : search system wide [on NUMA system] )
 
+The system default is architecture dependent.  The system default
+can be changed using the relax_domain_level= boot parameter.
+
 This file is per-cpuset and affect the sched domain where the cpuset
 belongs to.  Therefore if the flag 'sched_load_balance' of a cpuset
 is disabled, then 'sched_relax_domain_level' have no effect since