Sort of get config to work

src/DependencyInjection/Configuration.php

@@ -0,0 +1,30 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Pcm\IconBundle\DependencyInjection;
+
+use Symfony\Component\Config\Definition\Builder\TreeBuilder;
+use Symfony\Component\Config\Definition\ConfigurationInterface;
+
+class Configuration implements ConfigurationInterface
+{
+    public function getConfigTreeBuilder(): TreeBuilder
+    {
+        $treeBuilder = new TreeBuilder('pcm_icon');
+
+        $treeBuilder->getRootNode()
+            ->children()
+                ->arrayNode('directories')
+                    ->scalarPrototype()
+                        ->end()
+                    ->end()
+                ->arrayNode('palletes')->variablePrototype()->end()
+
+                    ->end()
+            ->end()
+        ;
+
+        return $treeBuilder;
+    }
+}