http: comment tweaks

It hasn't been primitive in a while.

R=golang-dev, adg
CC=golang-dev
https://golang.org/cl/5287041

src/pkg/http/client.go

@@ -2,7 +2,10 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// Primitive HTTP client. See RFC 2616.
+// HTTP client. See RFC 2616.
+// 
+// This is the high-level Client interface.
+// The low-level implementation is in transport.go.
 
 package http
 

src/pkg/http/transport.go

@@ -2,6 +2,11 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+// HTTP client implementation. See RFC 2616.
+// 
+// This is the low-level Transport implementation of RoundTripper.
+// The high-level interface is in client.go.
+
 package http
 
 import (