minor #9606 [Encore] Encore.configureUrlLoader() documentation (Lyrkan, javiereguiluz)

This PR was merged into the 3.4 branch.

Discussion
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[Encore] Encore.configureUrlLoader() documentation

This PR adds the documentation for the `Encore.configureUrlLoader()` method (symfony/webpack-encore#296).

Not sure if it should be more detailed since the other options of the URL loader are typically not needed...

Commits
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5c87901 Use the default article title
4d8700f Reword
6820867 Encore.configureUrlLoader() documentation

Author: javiereguiluz

frontend.rst

@@ -53,6 +53,7 @@ Optimizing
 * :doc:`Versioning (and the manifest.json file) </frontend/encore/versioning>`
 * :doc:`Using A CDN </frontend/encore/cdn>`
 * :doc:`Creating a "Shared" entry for re-used modules </frontend/encore/shared-entry>`
+* :doc:`/frontend/encore/url-loader`
 
 Guides
 ......

frontend/encore/url-loader.rst

@@ -0,0 +1,51 @@
+Inlining files in CSS with Webpack URL Loader
+=============================================
+
+A simple technique to improve the performance of web applications is to reduce
+the number of HTTP requests inlining small files as base64 encoded URLs in the
+generated CSS files.
+
+Webpack Encore provides this feature via Webpack's `URL Loader`_ plugin, but
+it's disabled by default. First, add the URL loader to your project:
+
+.. code-block:: terminal
+
+    $ yarn add --dev url-loader
+
+Then enable it in your ``webpack.config.js``:
+
+.. code-block:: javascript
+
+    // webpack.config.js
+    // ...
+
+    Encore
+        // ...
+        .configureUrlLoader({
+            fonts: { limit: 4096 },
+            images: { limit: 4096 }
+        })
+    ;
+
+The ``limit`` option defines the maximum size in bytes of the inlined files. In
+the previous example, font and image files having a size below or equal to 4 KB
+will be inlined and the rest of files will be processed as usual.
+
+You can also use all the other options supported by the `URL Loader`_. If you
+want to disable this loader for either images or fonts, remove the corresponding
+key from the object that is passed to the ``configureUrlLoader()`` method:
+
+.. code-block:: javascript
+
+    // webpack.config.js
+    // ...
+
+    Encore
+        // ...
+        .configureUrlLoader({
+            // 'fonts' is not defined, so only images will be inlined
+            images: { limit: 4096 }
+        })
+    ;
+
+.. _`URL loader`: https://github.com/webpack-contrib/url-loader