title: create-react-app with typescript - how to put types in separate file
body: <p>I'm using CRA with typescript (<code>create-react-app myapp --typescript</code>)</p>
  
  <p>I have some typescript stuff in my <code>App.tsx</code> that I would like to store externally, and I've tried creating <code>App.d.ts</code>, <code>index.d.ts</code>, <code>module.d.ts</code> and none of it works.</p>
  
  <p>Here's the interface I'm using:</p>
  
  <pre><code>declare interface IArgs {
      home: string,
      away: string
  }
  </code></pre>
  
  <p>What do I need to do to be able to declare all my Typescript stuff in a file that my source files can share?</p>