feat: Add file names to snippets

contents/tab.mdx

@@ -9,7 +9,7 @@ title: Tab
 
 ## HTML
 
-```html
+```html index.html
 <div class="tab">
     <!-- Active tab -->
     <div class="tab__item tab__item--active">...</div>
@@ -21,7 +21,7 @@ title: Tab
 
 ## CSS
 
-```css
+```css styles.css
 .tab {
     /* Center the content */
     align-items: center;