README.md

@@ -56,7 +56,13 @@ That is required, so we can safely provide Rust pointers through FFI. For that r
 
 [This project contains examples that can run in a desktop simulator.](./examples)
 
-To run the `demo` example:
+First of all you will have to pull lvgl submodule :
+```shell
+$ git submodule init
+$ git submodule update 
+```
+
+Then run the `demo` example:
 
 ```shell
 $ DEP_LV_CONFIG_PATH=`pwd`/examples/include cargo run --example demo