kmemleak: Add documentation on the memory leak detector

This patch adds the Documentation/kmemleak.txt file with some
information about how kmemleak works.

Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 4a3c220..04a44cc 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -1077,6 +1077,10 @@
 			Configure the RouterBoard 532 series on-chip
 			Ethernet adapter MAC address.
 
+	kmemleak=	[KNL] Boot-time kmemleak enable/disable
+			Valid arguments: on, off
+			Default: on
+
 	kstack=N	[X86] Print N words from the kernel stack
 			in oops dumps.