diff --git a/docker-exec-via-sock.sh b/docker-exec-via-sock.sh
index ab7a18f..21e0004 100755
--- a/docker-exec-via-sock.sh
+++ b/docker-exec-via-sock.sh
@@ -2,6 +2,7 @@
 set -eu
 
 # 通过 Docker Engine unix 套接字在容器中执行命令。
+# Docker Engine API: https://docs.docker.com/reference/api/engine/
 # 示例: ./docker-exec-via-sock.sh --container=my-container --cmd="ls -l /"
 
 log() {