update readme

README.md

@@ -15,7 +15,14 @@ You need to have the `cryptography` python library available on the localhost an
 
 ## How to use it
 
-Copy the roles of the repo in the role folder of your ansible projet. Define in you projet the variables you want/need to modify (cf the section Generate a CA).
+Add the submodule of the role you want to use in your role folder:
+
+```
+git submodule add ssh://git@gitea.auro.re:2222/Pains-Perdus/generate-cert.git roles/generate-cert
+git submodule init
+```
+
+Define in you projet the variables you want/need to modify (cf the section Generate a CA).
 
 After that you can use the role in your playbooks, as shown in the example playbook.