title: what is the syntax of 'unarchive' of the jenkins workflow plugin?
body: <p>I see multiple usages of <code>unarchive</code> in the <a href="https://github.com/jenkinsci/workflow-plugin/blob/master/TUTORIAL.md" rel="noreferrer">tutorial of the Jenkins workflow plugin</a>.
  But I'm not able to find any documentation about its syntax and options.</p>