add buttons and eventListeners

docs/bundle.js

@@ -0,0 +1,10 @@
+var s = document.querySelectorAll("pre");
+s.forEach(element => {
+    var button = document.createElement("button");
+    button.innerHTML = "Copy to clipboard";
+    element.parentElement.appendChild(button);
+
+    button.addEventListener ("click", function() {
+        console.log(element.textContent);
+      });
+});