How to use app.config with Visual Studio add-in?

using (IsolatedStorageFile file = IsolatedStorageFile.GetUserStoreForAssembly())
    {
       using (StreamWriter stream = new StreamWriter(new IsolatedStorageFileStream("YourConfig.xml", FileMode.Create, file)))
       {
          stream.Write(YourXmlDocOfConfiguration);
       }
       stream.Flush();
       stream.Close();
     }

string yourConfigXmlString;
    using (IsolatedStorageFile file = IsolatedStorageFile.GetUserStoreForAssembly())
    {
       string[] files = file.GetFileNames("YourConfig.Xml");
       if (files.Length > 0 && files[0] == "YourConfig.xml"))
       {
          using (StreamReader stream = new StreamReader(new IsolatedStorageFileStream("YourConfig.xml", FileMode.Open, file)))
          {
            yourConfigXmlString = stream.ReadToEnd();
          }
       }
     }