add lfs instructions

README.md

@@ -6,6 +6,13 @@ The best FPS you've ever seen !
 
 Install xmake from [here](https://xmake.io/#/guide/installation).
 
+## Cloning
+
+You need git lfs.
+
+If cloning with ssh, you should `git config --global http.sslCAInfo ~/.ssh/id_rsa` first,
+else lfs will fail to download the assets
+
 ## How to use
 
 You must have [godot](https://godotengine.org/) in your path
@@ -31,4 +38,4 @@ xmake clean
 # by default the generated files will save under "src" folder, you can change it by -d folder/under/src
 xmake ext-class -n MySprite2D -b Sprite2D -s myexample1 -d sample
 
-```
+```