title: How to describe model of mobx-state-tree with interface of typescript?
body: <p>I have some interfaces already, and I want to describe models with this interfaces, just like the code below. Otherwise I have to write again by using <code>types</code> of <code>mobx-state-tree</code>.  But this is not the right way, what is the valid solution ?</p>
  
  <pre><code>    import { types } from 'mobx-state-tree';
  
      export interface IPeople {
        name: string;
        age: number;
      }
  
      const Peoples = types
        .model({
          name: 'peoples',
          nancy: IPeople, // error at this line
        })
  
      export default Peoples;
  </code></pre>