docs: fix heading levels

Author: AriPerkkio

docs/tutorialkit.dev/src/content/docs/reference/configuration.mdx

@@ -426,7 +426,7 @@ type DownloadAsZip =
 
 ```
 
-##### `meta`
+### `meta`
 
 Configures `<meta>` tags for Open Graph protocole and Twitter.
 TutorialKit will use your logo as the default image.
@@ -456,7 +456,7 @@ If your logo uses the SVG format, it may not display on most social platforms.
 Use a raster format instead, such as WEBP or PNG.
 :::
 
-##### `custom`
+### `custom`
 
 Assign custom fields to a chapter/part/lesson.
 <PropertyTable inherited type="Record<string,any>" />