add the option to specify the family per rule to support ipv6 (#3)

Closes: #2 

* add the option to specify the family per rule to support ipv6

* include policy updates for ipv6

* update documentation to mention ipv6

* Make ipv6 optional; remove spurious tabs from the readme.

* set ipv6 policies only if ipv6 is enabled on the host and not explicitly turned off for this service
diff --git a/README.rst b/README.rst
index 5a046d8..5024293 100644
--- a/README.rst
+++ b/README.rst
@@ -22,6 +22,7 @@
     parametetrs:
       iptables:
         service:
+          enabled: True
           chain:
             INPUT:
               rules:
@@ -88,6 +89,24 @@
                   source_network: 192.168.1.0/24
                   jump: ACCEPT
 
+IPv6 is supported as well
+
+.. code-block:: yaml
+
+    parameters:
+      iptables:
+        service:
+          enabled: True
+          ipv6: True
+          chain:
+            INPUT:
+              rules:
+                - protocol: tcp
+                  family: ipv6
+                  destination_port: 22
+                  source_network: 2001:DB8::/32
+                  jump: ACCEPT
+
 Read more
 =========