test: explanatory comments [c-g]*

R=golang-dev, bradfitz
CC=golang-dev
https://golang.org/cl/5656103
diff --git a/test/for.go b/test/for.go
index a21213f..8a50090 100644
--- a/test/for.go
+++ b/test/for.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 for loops.
+
 package main
 
 func assertequal(is, shouldbe int, msg string) {