add code blocks + copy

js/copy-code.js

@@ -0,0 +1,7 @@
+for (let button of document.querySelectorAll(".copy-code")) {
+  button.addEventListener("click", async () => {
+    await navigator.clipboard.writeText(button.value)
+    button.textContent = "Copied!"
+    setTimeout(() => {button.textContent = "Copy"}, 1000.0)
+  })
+}