test/[n-z]*.go: add documentation

R=golang-dev, bradfitz, r
CC=golang-dev
https://golang.org/cl/5700056
diff --git a/test/sinit.go b/test/sinit.go
index 5cd3a45..1bc2810 100644
--- a/test/sinit.go
+++ b/test/sinit.go
@@ -4,6 +4,9 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+// Test that many initializations can be done at link time and
+// generate no executable init functions.
+
 package p
 
 // Should be no init func in the assembly.