title: Pass value to NLog custom LayoutRenderer
body: <p>Ok，now I knew how to write a custom <strong>layoutRender</strong> </p>
  
  <ol>
  <li>write a class <strong>MylayoutRender</strong> inherits <strong>LayoutRenderer</strong>, in class,  </li>
  <li>override <strong>Append</strong> method</li>
  <li><p>register custom layoutRenderer on startup</p>
  
  <p><code>ConfigurationItemFactory.Default.LayoutRenderers.RegisterDefinition("application", typeof(MyLayoutRenderer));</code></p></li>
  </ol>
  
  <p>curently, I read the value from config</p>
  
  <pre><code>protected override void Append(StringBuilder builder, LogEventInfo logEvent)
      {
          var product = CommonMethods.ReadConfig("product");
          builder.Append(product); 
      }
  </code></pre>
  
  <p>how to set the value dynamically?</p>