test: document ken/*.go

R=golang-dev, rsc
CC=golang-dev
https://golang.org/cl/5694065
diff --git a/test/ken/divconst.go b/test/ken/divconst.go
index 46786fb..670e074 100644
--- a/test/ken/divconst.go
+++ b/test/ken/divconst.go
@@ -4,6 +4,8 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+// Test integer division by constants.
+
 package main
 
 import "math/rand"