names: Add information about adding static domains/subdomains

Tests:

- Visit the add static domain page. Notice that additional form description is
visible.

Signed-off-by: Sunil Mohan Adapa <sunil@medhas.org>
Reviewed-by: James Valleroy <jvalleroy@mailbox.org>

plinth/modules/names/templates/names-domain-add.html

@@ -0,0 +1,25 @@
+{% extends "form.html" %}
+{% comment %}
+# SPDX-License-Identifier: AGPL-3.0-or-later
+{% endcomment %}
+
+{% load bootstrap %}
+{% load i18n %}
+
+{% block form_description %}
+  <p>
+    {% blocktrans trimmed %}
+      If you purchased a domain name from a domain registrar, you can configure
+      it here. The name servers responsible for the domain must be pointing (A
+      and AAAA records) to the public IP addresses of the {{ box_name }}.
+    {% endblocktrans %}
+  </p>
+  <p>
+    {% blocktrans trimmed %}
+      If you wish to also use a subdomian of an already configured domain, add
+      another entry for it here. Ensure that the subdomain is configured to
+      point to {{ box_name }}. Subdomains are useful for hosting multiple
+      applications that each require a dedicted domain for themselves.
+    {% endblocktrans %}
+  </p>
+{% endblock %}

plinth/modules/names/views.py

@@ -106,7 +106,7 @@ class HostnameView(FormView):
 
 class DomainAddView(FormView):
     """View to update system's static domain name."""
-    template_name = 'form.html'
+    template_name = 'names-domain-add.html'
     form_class = DomainAddForm
     prefix = 'domain-add'
     success_url = reverse_lazy('names:index')

plinth/templates/form.html

@@ -10,6 +10,9 @@
 
   <h3>{{ title }}</h3>
 
+  {% block form_description %}
+  {% endblock %}
+
   <form class="form form-{{ form.prefix }}" method="post">
     {% csrf_token %}