test: explanatory comments [c-g]*

R=golang-dev, bradfitz
CC=golang-dev
https://golang.org/cl/5656103
diff --git a/test/func5.go b/test/func5.go
index 68ab7a5..2e058be 100644
--- a/test/func5.go
+++ b/test/func5.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 functions and goroutines.
+
 package main
 
 func caller(f func(int, int) int, a, b int, c chan int) {