Merge branch '3.4' into 4.4

* 3.4:
  Update installation.rst

Author: javiereguiluz

frontend/encore/installation.rst

@@ -129,14 +129,24 @@ is the main config file for both Webpack and Webpack Encore:
 
     module.exports = Encore.getWebpackConfig();
 
-Next, create a new ``assets/js/app.js`` file with some basic JavaScript *and*
-import some CSS:
+Next, open the new ``assets/js/app.js`` file which contains some JavaScript code
+*and* imports some CSS:
 
 .. code-block:: javascript
 
     // assets/js/app.js
-
-    require('../css/app.css');
+    /*
+     * Welcome to your app's main JavaScript file!
+     *
+     * We recommend including the built version of this JavaScript file
+     * (and its CSS file) in your base layout (base.html.twig).
+     */
+
+    // any CSS you import will output into a single css file (app.css in this case)
+    import '../css/app.css';
+
+    // Need jQuery? Install it with "yarn add jquery", then uncomment to import it.
+    // import $ from 'jquery';
 
     console.log('Hello Webpack Encore! Edit me in assets/js/app.js');