kernel/sysctl.c: finish off the warning comments

I've been chasing these comments around this file all week.  Hopefully we're
straight now.
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

kernel/sysctl.c

@@ -748,7 +748,10 @@ static ctl_table kern_table[] = {
 		.proc_handler	= &proc_dostring,
 		.strategy	= &sysctl_string,
 	},
-
+/*
+ * NOTE: do not add new entries to this table unless you have read
+ * Documentation/sysctl/ctl_unnumbered.txt
+ */
 	{ .ctl_name = 0 }
 };