title: Add Property to Object that is returned by Sequelize FindOne
body: <p>I am trying to add a property to a sequelize instance before passing it back to the client. </p>
  
  <pre><code>router.get('/cats/1', function (req, res) {
      Cat.findOne({where: {id: 1}})
          .then(function (cat) {
              // cat exists and looks like {id: 1}
              cat.name = "Lincoln";
              // console.log of cat is {id: 1, name: Lincoln}
              res.json(cat);
          });
  });
  </code></pre>
  
  <p>The client only see's <code>{id: 1}</code> and not the newly added key. </p>
  
  <ul>
  <li>What is going on here? </li>
  <li>What type of Object is returned by Sequelize? </li>
  <li>How can I add new properties to my Cats and send them back? </li>
  </ul>