diff --git a/README.md b/README.md
index 061b412..f9c7b60 100644
--- a/README.md
+++ b/README.md
@@ -47,6 +47,8 @@ Generate self signed certificate:
 $ cargo r --example generate_self_signed_ca
 ```
 
+When generate success, cert and key will write to files `cert.pem`, `cert.key`.
+
 Important
 
 * Intermediate certificate tested: