go.net/spdy: add package description

R=golang-dev, dave
CC=golang-dev
https://golang.org/cl/6565062

spdy/types.go

@@ -2,6 +2,10 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+// Package spdy implements SPDY protocol which is descirbed in
+// draft-mbelshe-httpbis-spdy-00.
+//
+// http://tools.ietf.org/html/draft-mbelshe-httpbis-spdy-00
 package spdy
 
 import (