feat: Add copy joke button to clipboard functionality

dad-jokes/index.html

@@ -11,7 +11,8 @@
       <h3>Don't Laugh Challenge</h3>
       <div id="joke" class="joke">// Joke goes here</div>
       <button id="jokeBtn" class="btn">Get Another Joke</button>
+      <button class="btn copy-btn" id="copyBtn">Copy Joke</button>
     </div>
     <script src="script.js"></script>
   </body>
-</html>
+</html>