chore(readme): update

readme.md

@@ -8,7 +8,7 @@ A vue component for tree structure. Support adding treenode/leafnode, editing no
 # use
 ``npm install vue-tree-list``
 
-```javascript
+```html
 <template>
   <div>
     <button @click="addNode">Add Node</button>
@@ -32,6 +32,7 @@ A vue component for tree structure. Support adding treenode/leafnode, editing no
     </pre>
   </div>
 </template>
+
 <script>
   import { VueTreeList, Tree, TreeNode } from 'vue-tree-list'
   export default {
@@ -124,6 +125,7 @@ A vue component for tree structure. Support adding treenode/leafnode, editing no
     }
   }
 </script>
+
 <style lang="less" rel="stylesheet/less">
   .vtl {
     .vtl-drag-disabled {