title: productbuild: add third-party product archive to installer?
body: <p>I need to make Mac OS app installer, which also installs other third-party package.</p>
  
  <p>When trying to add it via productbuild --synthesize, it tells "ThirdPartyPackage.pkg is a product archive, not a component package".</p>
  
  <p>So, how should I correctly insert third-party product installer into my installer?</p>