Update README.md

[patternhelloworld]

Update README.md to give a solution to preventing an error message "Unable to join channel. Member data for presence channel missing."

There is additoinal info on the code below. Link

    public function broadcast(Request $request)
    {
        $channel_name = $request['channel_name'];

        $user = $request->user()->toArray();
        $user['user_id'] = $user['id'];
        $user['user_info'] = $user;
        return response()->json(['channel_data' => $user], 200);

    }