Add docblock

src/Twig/Runtime/IconRuntime.php

@@ -104,6 +104,9 @@ final class IconRuntime implements RuntimeExtensionInterface
         $this->removeBlackFillAttributes($svg);
     }
 
+    /**
+     * @throws IconNotFound when an svg file with the passed in name cannot be found
+     */
     private function findSvgFilepath(string $iconName): string
     {
         foreach ($this->directories as $directory) {