ksm: add some documentation

Add Documentation/vm/ksm.txt: how to use the Kernel Samepage Merging feature

Signed-off-by: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: Michael Kerrisk <mtk.manpages@googlemail.com>
Cc: Randy Dunlap <randy.dunlap@oracle.com>
Acked-by: Izik Eidus <ieidus@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/Documentation/vm/00-INDEX b/Documentation/vm/00-INDEX
index 2f77ced..f80a449 100644
--- a/Documentation/vm/00-INDEX
+++ b/Documentation/vm/00-INDEX
@@ -6,6 +6,8 @@
 	- various information on memory balancing.
 hugetlbpage.txt
 	- a brief summary of hugetlbpage support in the Linux kernel.
+ksm.txt
+	- how to use the Kernel Samepage Merging feature.
 locking
 	- info on how locking and synchronization is done in the Linux vm code.
 numa