test: document ken/*.go

R=golang-dev, rsc
CC=golang-dev
https://golang.org/cl/5694065
diff --git a/test/ken/array.go b/test/ken/array.go
index 53f6fc8..9412e35 100644
--- a/test/ken/array.go
+++ b/test/ken/array.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 arrays and slices.
+
 package main
 
 func setpd(a []int) {