Add note about no_log use on vault data retrieve.

When using the ipavault module to retrieve stored data, this data is
often sensitive, and if `no_log` is not enabled on the playbook, the
sensitive data will be logged by Ansible.

This change in de documentation, and playbook examples, suggests the
use of `no_log: true` when using `state: retrieved` with ipavault.

playbooks/vault/retrive-data-asymmetric-vault.yml

@@ -13,5 +13,6 @@
         private_key_file: private.pem
         state: retrieved
       register: result
+      no_log: true
     - debug:
        msg: "Data: {{ result.vault.data }}"