Add usage

README.md

@@ -19,6 +19,16 @@ Add to your requirements.yml file a role entry like:
 
 # Usage
 
+Create a playbook like:
+
+```yaml
+---
+- name: Configure OpenDKIM in mail servers
+  hosts: mail_servers[0]
+  roles:
+    - role: opendkim_postfix
+```
+
 Set at least a list of domain names with the variable mail_domains. If you have an OVH account for your DNS domains you can add the variables related (check defaults/main.yml).
 
 # Credits