feat: Add file names to snippets

contents/sticky-header.mdx

@@ -9,7 +9,7 @@ title: Sticky header
 
 ## HTML
 
-```html
+```html index.html
 <div>
     <header class="sticky-header__header">...</header>
     <main>...</main>
@@ -18,7 +18,7 @@ title: Sticky header
 
 ## CSS
 
-```css
+```css styles.css
 .sticky-header__header {
     /* Stick to the top */
     position: sticky;