doc: add docker pull icon

Author: guangzhengli

README.md

@@ -1,6 +1,6 @@
 <h1 align=center>Kubernetes Tutorials ｜ k8s 教程</h1>
 
-[![GitHub forks](https://img.shields.io/github/forks/guangzhengli/k8s-tutorials)](https://github.com/guangzhengli/k8s-tutorials/network)[![GitHub stars](https://img.shields.io/github/stars/guangzhengli/k8s-tutorials)](https://github.com/guangzhengli/k8s-tutorials/stargazers)[![GitHub issues](https://img.shields.io/github/issues/guangzhengli/k8s-tutorials)](https://github.com/guangzhengli/k8s-tutorials/issues)[![GitHub license](https://img.shields.io/github/license/guangzhengli/k8s-tutorials)](https://github.com/guangzhengli/k8s-tutorials/blob/main/LICENSE)
+[![GitHub forks](https://img.shields.io/github/forks/guangzhengli/k8s-tutorials)](https://github.com/guangzhengli/k8s-tutorials/network)[![GitHub stars](https://img.shields.io/github/stars/guangzhengli/k8s-tutorials)](https://github.com/guangzhengli/k8s-tutorials/stargazers)[![GitHub issues](https://img.shields.io/github/issues/guangzhengli/k8s-tutorials)](https://github.com/guangzhengli/k8s-tutorials/issues)[![GitHub license](https://img.shields.io/github/license/guangzhengli/k8s-tutorials)](https://github.com/guangzhengli/k8s-tutorials/blob/main/LICENSE)![Docker Pulls](https://img.shields.io/docker/pulls/guangzhengli/hellok8s)
 
 <h4 align=center>🌈 Kubernetes | 📰 Tutorials</h4>