Docs for react-router v4 basename feature (#2668)

* Docs for react-router v4 basename feature

Fix https://github.com/facebookincubator/create-react-app/issues/2593

* Update README.md

* Update README.md

* Update README.md

* Update README.md

packages/react-scripts/template/README.md

@@ -1776,6 +1776,15 @@ To override this, specify the `homepage` in your `package.json`, for example:
 
 This will let Create React App correctly infer the root path to use in the generated HTML file.
 
+**Note**: If you are using `react-router@^4`, you can root `<Link>`s using the `basename` prop on any `<Router>`.<br>
+More information [here](https://reacttraining.com/react-router/web/api/BrowserRouter/basename-string).<br>
+<br>
+For example:
+```js
+<BrowserRouter basename="/calendar"/>
+<Link to="/today"/> // renders <a href="/calendar/today">
+```
+
 #### Serving the Same Build from Different Paths
 
 >Note: this feature is available with `react-scripts@0.9.0` and higher.