diff --git a/README.md b/README.md
index e64acb9..7fc844a 100644
--- a/README.md
+++ b/README.md
@@ -71,9 +71,12 @@ location /.well-known/acme-challenge/ {
 
 通过命令行交互创建DNS挑战证书：
 ```shell
-acme-client --allow-interact -t dns --email email@example.com -d example.net
+acme-client --port 0 -t dns --allow-interact --email email@example.com -d example.net
 ```
 
+* `email@example.com` -- your email
+* `example.net` -- your domain
+
 出现以下提示时需要自行配置DNS，配置完成后按"回车"：
 ```shell
 [INFO ] You need to config dns manually, press enter to continue...