fix two lines of command

Author: panpan0000

docs/quick-start-in-china.md

@@ -1,8 +1,7 @@
 # Quick Start in China
 
-If the machine is in China, you should replace the command to:
+If the machine is in China, you should replace the command as below(to use registry mirror: docker.m.daocloud.io):
 
 ```
-helm install -n kube-node-tuning kube-node-tuning kube-node-tuning/kube-node-tuning --create-namespace
- --set image.registry=docker.m.daocloud.io
+helm install -n kube-node-tuning kube-node-tuning kube-node-tuning/kube-node-tuning --create-namespace --set image.registry=docker.m.daocloud.io
 ```