Document usage of name_from_ip.

Since `name_from_ip` has a similar, but not equal, behavior to `name`,
and as the inferred DNS zone might depend on DNS configuration and
can be different than the user expects, it has some limited usage,
and the user must be aware of its effects.

This change to the documentation enhance the documentation including
more details on the attribute usage.

README-dnszone.md

@@ -152,6 +152,46 @@ Example playbook to remove a zone:
 
 ```
 
+Example playbook to create a zone for reverse DNS lookup, from an IP address:
+
+```yaml
+
+---
+- name: dnszone present
+  hosts: ipaserver
+  become: true
+
+  tasks:
+  - name: Ensure zone for reverse DNS lookup is present.
+    ipadnszone:
+      ipaadmin_password: SomeADMINpassword
+      name_from_ip: 192.168.1.2
+      state: present
+```
+
+Note that, on the previous example the zone created with `name_from_ip` might be "1.168.192.in-addr.arpa.", "168.192.in-addr.arpa.", or "192.in-addr.arpa.", depending on the DNS response the system get while querying for zones, and for this reason, when creating a zone using `name_from_ip`, the inferred zone name is returned to the controller, in the attribute `dnszone.name`. Since the zone inferred might not be what a user expects, `name_from_ip` can only be used with `state: present`. To have more control over the zone name, the prefix length for the IP address can be provided.
+
+Example playbook to create a zone for reverse DNS lookup, from an IP address, given the prefix length and displaying the resulting zone name:
+
+```yaml
+
+---
+- name: dnszone present
+  hosts: ipaserver
+  become: true
+
+  tasks:
+      - name: Ensure zone for reverse DNS lookup is present.
+    ipadnszone:
+      ipaadmin_password: SomeADMINpassword
+      name_from_ip: 192.168.1.2/24
+      state: present
+    register: result
+  - name: Display inferred zone name.
+    debug:
+      msg: "Zone name: {{ result.dnszone.name }}"
+```
+
 
 Variables
 =========
@@ -164,7 +204,7 @@ Variable | Description | Required
 `ipaadmin_principal` | The admin principal is a string and defaults to `admin` | no
 `ipaadmin_password` | The admin password is a string and is required if there is no admin ticket available on the node | no
 `name` \| `zone_name` | The zone name string or list of strings. | no
-`name_from_ip` | Derive zone name from reverse of IP (PTR). | no
+`name_from_ip` | Derive zone name from reverse of IP (PTR). Can only be used with `state: present`. | no
 `forwarders` | The list of forwarders dicts. Each `forwarders` dict entry has:| no
   | `ip_address` - The IPv4 or IPv6 address of the DNS server. | yes
   | `port` - The custom port that should be used on this server. | no

plugins/modules/ipadnszone.py

@@ -44,7 +44,9 @@ options:
     type: list
     alises: ["zone_name"]
   name_from_ip:
-    description: Derive zone name from reverse of IP (PTR).
+    description: |
+      Derive zone name from reverse of IP (PTR).
+      Can only be used with `state: present`.
     required: false
     type: str
   forwarders: