title: Pymodm - Mongodb, How to create an index in a collection
body: <p>I'm trying to create server side flask session extension that expires after # time. I found below <code>Mongodb</code> shell command in the documentation.</p>
  
  <pre><code>db.log_events.createIndex( { "createdAt": 1 }, { expireAfterSeconds: 3600 } )
  </code></pre>
  
  <p>But how can I do it using <code>pymodm</code>? </p>