feat: Add file names to snippets

contents/sticky-footer.mdx

@@ -9,7 +9,7 @@ title: Sticky footer
 
 ## HTML
 
-```html
+```html index.html
 <div class="sticky-footer">
     <header class="sticky-footer__header">...</header>
     <main class="sticky-footer__main">...</main>
@@ -19,7 +19,7 @@ title: Sticky footer
 
 ## CSS
 
-```css
+```css styles.css
 .sticky-footer {
     display: flex;
     flex-direction: column;