doc: move package top level synopsis to doc.go

Author: zchee

doc.go

@@ -0,0 +1,6 @@
+// Copyright 2020 The go-language-server Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Package jsonrpc2 is an implementation of the JSON-RPC 2 specification for Go.
+package jsonrpc2

jsonrpc2.go

@@ -2,7 +2,6 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// Package jsonrpc2 is an implementation of the JSON-RPC 2 specification for Go.
 package jsonrpc2
 
 import (