docs: update install guide

src/lazyload/README.md

@@ -6,7 +6,12 @@
 import Vue from 'vue';
 import { Lazyload } from 'vant';
 
-Vue.use(Lazyload, options);
+Vue.use(Lazyload);
+
+// with options
+Vue.use(Lazyload, {
+  lazyComponent: true
+});
 ```
 
 ## Usage

src/lazyload/README.zh-CN.md

@@ -8,8 +8,12 @@
 import Vue from 'vue';
 import { Lazyload } from 'vant';
 
-// options 为可选参数，无则不传
-Vue.use(Lazyload, options);
+Vue.use(Lazyload);
+
+// 注册时可以配置额外的选项
+Vue.use(Lazyload, {
+  lazyComponent: true
+});
 ```
 
 ## 代码演示