net/http: document net/http/cookiejar on CookieJar

R=golang-dev, nigeltao, adg
CC=golang-dev
https://golang.org/cl/7444048

src/pkg/net/http/jar.go

@@ -12,6 +12,8 @@ import (
 //
 // Implementations of CookieJar must be safe for concurrent use by multiple
 // goroutines.
+//
+// The net/http/cookiejar package provides a CookieJar implementation.
 type CookieJar interface {
 	// SetCookies handles the receipt of the cookies in a reply for the
 	// given URL.  It may or may not choose to save the cookies, depending