added installation infos in readme

README.md

@@ -1,6 +1,17 @@
 # cube3D
 ---
 
+### install
+---
+
+this project uses submodules recursively, so you after cloning you need to :
+
+`git submodule update --init --recursive`
+
+
+### presentation
+---
+
 This project is a 3D mini game, that uses raycasting to produce a FPP (first person perspective), something like Wolfenstein3D or Doom.
 
 ![moving into the 3D](assets/cube3d_aller_retour.gif)