组件添加add方法

packages/artplayer/src/layer.js

@@ -0,0 +1,13 @@
+import Component from './utils/component';
+
+export default class Layer extends Component {
+    constructor(art) {
+        super(art);
+        this.$parent = art.template.$layers;
+        art.on('ready', () => {
+            art.option.layers.forEach(item => {
+                this.add(item);
+            });
+        });
+    }
+}