Add example

README.md

@@ -18,6 +18,45 @@ composer require jsor/http-client-hints
 Check the [Packagist page](https://packagist.org/packages/jsor/http-client-hints) for all
 available versions.
 
+Example
+-------
+
+```php
+$resolved = (new Jsor\HttpClientHints\Resolver())
+    ->withWhitelist([
+        // Process only Width and DPR headers
+        'Width',
+        'DPR',
+    ])
+    ->withMapping([
+        // Map Width header to w key
+        'width'  => 'w',
+        // Needed to extract the height from the query params for recalculation depending on Width if present
+        'height' => 'h',
+    ])
+    ->resolve($_SERVER, $_GET)
+;
+
+if (isset($resolved['dpr'])) {
+    header('Content-DPR: ' . $resolved['dpr']);
+    header('Vary: DPR', false);
+}
+
+if (isset($resolved['w'])) {
+    header('Vary: Width', false);
+}
+
+// Use $resolved to generate thumbnails.
+// If you use Glide (https://github.com/thephpleague/glide), this could look
+// something like:
+
+$server = League\Glide\ServerFactory::create([
+    'source' => 'path/to/source/folder',
+    'cache' => 'path/to/cache/folder',
+]);
+$server->outputImage($path, array_merge($_GET, $resolved));
+```
+
 License
 -------