ipadnsforwardzone: Fix documentation for forwarders usage.

Examples of dnsforwarzone were using a single string rather than a
dict of values to set attribute `forwarders`. Both source code and
README examples were fixed.

Fix issue #446

plugins/modules/ipadnsforwardzone.py

@@ -89,8 +89,19 @@ EXAMPLES = '''
     state: present
     name: example.com
     forwarders:
-    - 8.8.8.8
-    - 4.4.4.4
+    - ip_address: 8.8.8.8
+    - ip_address: 4.4.4.4
+    forwardpolicy: first
+    skip_overlap_check: true
+
+# Ensure dns zone is present, with forwarder on non-default port
+- ipadnsforwardzone:
+    ipaadmin_password: MyPassword123
+    state: present
+    name: example.com
+    forwarders:
+    - ip_address: 8.8.8.8
+      port: 8053
     forwardpolicy: first
     skip_overlap_check: true