[Frontend] Mention configureBabelPresetEnv()

Author: javiereguiluz

frontend/encore/babel.rst

@@ -49,6 +49,23 @@ cache directory:
     # On Unix run this command. On Windows, clear this directory manually
     $ rm -rf node_modules/.cache/babel-loader/
 
+If you want to customize the ``preset-env`` configuration, use the ``configureBabelPresetEnv()``
+method as follows:
+
+.. code-block:: javascript
+
+    // webpack.config.js
+    // ...
+
+    Encore
+        // ...
+
+        .configureBabelPresetEnv((config) => {
+            config.useBuiltIns = 'usage';
+            config.corejs = 3;
+        })
+    ;
+
 Creating a ``.babelrc`` File
 ----------------------------