Add docker server registry

Author: kartik494

content/en/docs/concepts/configuration/secret.md

@@ -201,7 +201,8 @@ to create a Docker registry Secret, you can do:
 kubectl create secret docker-registry secret-tiger-docker \
   --docker-username=tiger \
   --docker-password=pass113 \
-  [email protected]
+  [email protected] \
+  --docker-server=my-registry:5000
 ```
 
 This command creates a Secret of type `kubernetes.io/dockerconfigjson`.