feat: Add file names to snippets

contents/stacked-cards.mdx

@@ -9,7 +9,7 @@ title: Stacked cards
 
 ## HTML
 
-```html
+```html index.html
 <div class="stacked-cards">
     <!-- Repeat if you want to have more cards -->
     <div class="stacked-cards__card"></div>
@@ -21,7 +21,7 @@ title: Stacked cards
 
 ## CSS
 
-```css
+```css styles.css
 .stacked-cards {
     /* Used to position the stacked cards */
     position: relative;