update doc (#3)

cppcoffee · web-flow · commit 8c92398d5d41 · 2023-04-23T11:05:14.000+08:00
Signed-off-by: Xiaobo Liu &lt;cppcoffee@gmail.com&gt;
diff --git a/README.md b/README.md
@@ -7,6 +7,7 @@ Block ip behavior use XDP package drop.
 ### Build
 
 ```shell
+$ git submodule init
 $ git submodule update
 $ make
 ```
