fix: new examples in README

README.md

@@ -18,11 +18,22 @@ None
 
 ## How to use
 
-```
-- hosts: dns-server
-  vars:
+ * `host_vars/dns-master`
+ ```
  bind_role: master
-    bind_zones:
+ ```
+
+ * `host_vars/dns-slave`
+ ```
+ bind_role: slave
+ ```
+
+ * `group_vars/dns-server`
+ ```
+bind_listen_ipv6: true
+bind_listen_ipv4: true
+
+bind_zones:
   test.local:
     ns_primary: ns1.test.local
     mail: root@test.local
@@ -39,6 +50,12 @@ None
     entries:
       - { name: '@', type: ns, value: localhost. }
       - { name: hello, type: a, value: 4.3.2.1 }
+ ```
+
+ * playbook
+
+```
+- hosts: dns-server
   roles:
     - bind 
 ```