Doc: Improve recipes documentation

README.md

@@ -209,8 +209,50 @@ $etl = (new EtlExecutor())
 
 This will basically listen to all events and fire log entries.
 
+### Creating your own recipes
 You can create your own recipes by implementing `BenTools\ETL\Recipe\Recipe` or using a callable with the same signature.
 
+Example for displaying a progress bar when using the Symfony framework:
+
+```php
+use BenTools\ETL\EtlExecutor;
+use BenTools\ETL\EventDispatcher\Event\Event;
+use BenTools\ETL\Recipe\Recipe;
+use Symfony\Component\Console\Helper\ProgressBar;
+
+final class ProgressBarRecipe extends Recipe
+{
+    public function __construct(
+        public readonly ProgressBar $progressBar,
+    ) {
+    }
+
+    public function decorate(EtlExecutor $executor): EtlExecutor
+    {
+        return $executor
+            ->onStart(function (Event $event) {
+                if (!$event->state->nbTotalItems) {
+                    return;
+                }
+                $this->progressBar->setMaxSteps($event->state->nbTotalItems);
+            })
+            ->onExtract(fn () => $this->progressBar->advance())
+            ->onEnd(fn () => $this->progressBar->finish());
+    }
+}
+```
+
+Usage:
+
+```php
+use BenTools\ETL\EtlExecutor;
+use Symfony\Component\Console\Style\SymfonyStyle;
+
+$output = new SymfonyStyle($input, $output);
+$progressBar = $output->createProgressBar();
+$executor = (new EtlExecutor())->withRecipe(new ProgressBarRecipe());
+```
+
 Contribute
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