title: Firestore - batch.add is not a function
body: <p>The <a href="https://firebase.google.com/docs/firestore/manage-data/transactions#batched-writes" rel="noreferrer">documentation</a> for Firestore batch writes lists only <code>set()</code>, <code>update()</code> and <code>delete()</code> as permitted operations.</p>
  
  <p>Is there no way to add an <code>add()</code> operation to the batch? I need a document to be created with an auto-generated id.</p>