Update README.md, remove migration.php, add message to browser.php

browser.php

@@ -6,6 +6,10 @@ use Illuminate\Database\Capsule\Manager as Capsule;
 use Krzysiej\RyobiCrawler\Models\Product;
 use Twig\{Environment, Loader\FilesystemLoader};
 
+if (!file_exists('database.sqlite')) {
+    exit('Database file <code>database.sqlite</code> missing. Run docker compose <blockquote>docker compose exec php-app php index.php app:migrate</blockquote> to create it.');
+}
+
 $capsule = new Capsule;
 $capsule->addConnection(['driver' => 'sqlite', 'database' => __DIR__ . '/database.sqlite']);
 $capsule->setAsGlobal();