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/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 85c6f57..b52f47d 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -1679,6 +1679,10 @@
 			Format: <reboot_mode>[,<reboot_mode2>[,...]]
 			See arch/*/kernel/reboot.c or arch/*/kernel/process.c			
 
+	relax_domain_level=
+			[KNL, SMP] Set scheduler's default relax_domain_level.
+			See Documentation/cpusets.txt.
+
 	reserve=	[KNL,BUGS] Force the kernel to ignore some iomem area
 
 	reservetop=	[X86-32]