title: How to update local branch with arcanist when doing code review?
body: <p>Standard workflow in git to checkout code for review:</p>
  
  <ol>
  <li><code>git fetch -a &amp;&amp; git checkout branch-to-review</code></li>
  <li>Other engineer makes some changes and pushes to <code>branch-to-review</code>.</li>
  <li><code>git pull origin branch-to-review</code> to update your local copy to review.</li>
  </ol>
  
  <p>Workflow with Arcanist (via phabricator):</p>
  
  <ol>
  <li><code>arc patch D123456</code></li>
  <li>Other engineer makes some changes and pushes via <code>arc diff</code> on their end.</li>
  <li>???</li>
  </ol>
  
  <p>In step 3 where we are the code reviewer, how do we pull down the other engineer's most recent changes? <code>arc diff</code> locally seems to want to make more updates but from us. </p>
  
  <p><code>arc diff --update D123456</code> shows this warning:</p>
  
  <pre><code>You don't own revision D123456: "Added a new feature and made some updates". Normally, you should only update revisions you
  own. You can "Commandeer" this revision from the web interface if you
  want to become the owner.
  
  Update this revision anyway? [y/N] 
  </code></pre>
  
  <p>I can delete the local branch and patch it again, but that seems like the obviously wrong approach.</p>