Update docker pulls link in Readme file.

Update docker pulls link in Readme file.
diff --git a/README.md b/README.md
index 45ff2f6..e825ec3 100644
--- a/README.md
+++ b/README.md
@@ -2,6 +2,7 @@
 [![License](https://img.shields.io/badge/license-Apache%202-4EB1BA.svg)](https://www.apache.org/licenses/LICENSE-2.0.html)
 [![Average time to resolve an issue](http://isitmaintained.com/badge/resolution/apache/rocketmq-docker.svg)](http://isitmaintained.com/project/apache/rocketmq-docker "Average time to resolve an issue")
 [![Percentage of issues still open](http://isitmaintained.com/badge/open/apache/rocketmq-docker.svg)](http://isitmaintained.com/project/apache/rocketmq-docker "Percentage of issues still open")
+[![Docker Pulls](https://img.shields.io/docker/pulls/apache/rocketmq)](https://hub.docker.com/repository/docker/apache/rocketmq)
 ![Twitter Follow](https://img.shields.io/twitter/follow/ApacheRocketMQ?style=social)