feat: auto copy button code

assets/js/clipboard.js

@@ -1,8 +1,23 @@
 import Clipboard from 'clipboard';
 
-var clipboard = new Clipboard('.btn-clipboard');
+var pre = document.getElementsByTagName('pre');
+
+for (var i = 0; i < pre.length; ++ i)
+{
+  var element = pre[i];
+  element.insertAdjacentHTML('afterbegin', '<button class="btn btn-copy"></button>');
+}
+
+var clipboard = new Clipboard('.btn-copy', {
+
+  target: function(trigger) {
+    return trigger.nextElementSibling;
+  },
+
+});
 
 clipboard.on('success', function(e) {
+
     /*
     console.info('Action:', e.action);
     console.info('Text:', e.text);