title: How to include .d.ts file manually(locally)? Or How to use a user defined .d.ts file?
body: <p>I'm studying nuxt.js and due to some reason I want to extend Vue's instance like this:</p>
  <pre><code>import Vue from 'vue'
  
  Vue.prototype.$myProp = 'test'
  
  const app = new Vue()
  
  console.log(app.$myProp)
  </code></pre>
  <p>Following the guide at <a href="https://v2.vuejs.org/v2/guide/typescript.html#Augmenting-Types-for-Use-with-Plugins" rel="nofollow noreferrer">https://v2.vuejs.org/v2/guide/typescript.html#Augmenting-Types-for-Use-with-Plugins</a>, I have create a file at types/test.d.ts with the content bellow:</p>
  <pre><code>declare module 'vue/types/vue' {
    interface Vue {
      $myProp: string;
    }
  }
  </code></pre>
  <p>However, I don't know how to make it works.</p>
  <p>I was receiving errors in my VSCode. Also receive errors when I executing tsc(Version 3.7.2):</p>
  <pre><code>index.ts:14:17 - error TS2339: Property '$test' does not exist on type 'CombinedVueInstance&lt;Vue, object, object, object, Record&lt;never, any&gt;&gt;'.
  
  14 console.log(app.$test)
  </code></pre>
  <p>I have tried to using a tsconfig.json in the root directory, but not work:</p>
  <pre><code>{
      &quot;compilerOptions&quot;: {
          &quot;typeRoots&quot;: [
              &quot;types/test.d.ts&quot;
          ]
      }
  }
  </code></pre>
  <p>I have also tried insert a reference like this, but now work:</p>
  <pre><code>///&lt;reference path=&quot;types/test.d.ts&quot;/&gt;
  </code></pre>
  <p>Of course, I don't want to include this declare file in every file. Is there a way to enable the declare in whole project?</p>
  <p>I don't know how VSCode works with typescript. Maybe I just make a mistake in config file.</p>