Web Config Transformation to add a child element

I've got the following configuration in web.config:

  <resizer>
    <sizelimits imageWidth="0" />
    <plugins>
      <add name="MvcRoutingShim" />
      <!--<add name="AzureReader" connectionString="DataConnectionString" /> -->
      <add name="DiskCache" />
      <add name="PrettyGifs" />
      <add name="AnimatedGifs" />
    </plugins>
  </resizer>

In web.config.Release, how can I add the AzureReader element as a child of the plugins element (effectively uncommenting out the above)?

I'm familiar with how to do basic transformations but have never done this before.

You can use the Insert transformation:

 <resizer>
    <plugins>
      <add name="AzureReader" connectionString="DataConnectionString" 
           xdt:Transform="Insert" />
    </plugins>
  </resizer>

Web.config Transformation Syntax for Web Application Project Deployment