Fix #490 Make heading permalinks visible

Author: caendesilva

src/Services/MarkdownConverterService.php

@@ -74,7 +74,8 @@ protected function setupConverter(): void
                 'heading_permalink' =>[
                     'id_prefix' => '',
                     'fragment_prefix' => '',
-                    'symbol' => '',
+                    'symbol' => '#',
+                    'insert' => 'after'
                 ],
             ], $this->config);
         }