Add PWA description

Author: halfrost

README.md

@@ -24,19 +24,28 @@
 <img src="https://travis-ci.org/halfrost/LeetCode-Go.svg?branch=master">
 </p>
 
-<p align='center'>
+
 支持 Progressive Web Apps 的题解电子书《LeetCode Cookbook》 <a href="https://books.halfrost.com/leetcode/" rel="nofollow">Online Reading</a>
+
+<p align='center'>
+<a href="https://books.halfrost.com/leetcode/"><img src="https://img.halfrost.com/Leetcode/Cookbook_Safari.png"></a>
 </p>
 
+离线版本的电子书《LeetCode Cookbook》PDF <a href="https://github.com/halfrost/LeetCode-Go/releases/" rel="nofollow">Download here</a>
 
 <p align='center'>
-离线版本的电子书《LeetCode Cookbook》PDF <a href="https://github.com/halfrost/LeetCode-Go/releases/" rel="nofollow">Download here</a>
+<a href="https://github.com/halfrost/LeetCode-Go/releases/"><img src="https://img.halfrost.com/Leetcode/Cookbook.png"></a>
 </p>
 
+通过 iOS / Android 浏览器安装 PWA 版《LeetCode Cookbook》至设备桌面随时学习
+
 <p align='center'>
-<a href="https://github.com/halfrost/LeetCode-Go/releases/"><img src="https://img.halfrost.com/Leetcode/Cookbook.png"></a>
+<a href="https://books.halfrost.com/leetcode/"><img src="https://img.halfrost.com/Leetcode/Cookbook_PWA_iPad.png"></a>
+<a href="https://books.halfrost.com/leetcode/"><img src="https://img.halfrost.com/Leetcode/Cookbook_PWA_iPad_example1.png"></a>
+<a href="https://books.halfrost.com/leetcode/"><img src="https://img.halfrost.com/Leetcode/Cookbook_PWA_iPad_example2.png"></a>
 </p>
 
+
 ## Data Structures
 
 > 标识了 ✅ 的专题是完成所有题目了的，没有标识的是还没有做完所有题目的