title: create-react-app typescript global.d.ts file doesn't work
body: <p>I've got my <code>global.d.ts</code> file in <code>src</code> folder like this</p>
  
  <pre><code>declare global {
    interface Window {
      config: {
        url: string;
      };
    }
  }
  </code></pre>
  
  <p>Then somewhere in my components do</p>
  
  <pre><code>window.config = 'x';
  </code></pre>
  
  <p>And <code>ts</code> shows this error</p>
  
  <pre><code>Error:(10, 22) TS2339: Property 'config' does not exist on type 'Window'.
  </code></pre>
  
  <p>create-react-app is used for this app.</p>
  
  <pre><code>"react-scripts": "3.0.1",
  "typescript": "3.5.3"
  </code></pre>
  
  <p>This is how <code>tsconfig.json</code> looks like </p>
  
  <pre><code>{
    "compilerOptions": {
      "target": "es5",
      "lib": [
        "dom",
        "dom.iterable",
        "esnext"
      ],
      "allowJs": true,
      "skipLibCheck": true,
      "esModuleInterop": true,
      "allowSyntheticDefaultImports": true,
      "strict": true,
      "forceConsistentCasingInFileNames": true,
      "module": "esnext",
      "moduleResolution": "node",
      "resolveJsonModule": true,
      "isolatedModules": true,
      "noEmit": true,
      "jsx": "preserve"
    },
    "include": [
      "src"
    ]
  }
  </code></pre>