Add details about timings and direct integration

Outline how long it can take to integrate using the client documentation.

Add more detail about how to integrate directly with the API.

app/templates/views/documentation.html

@@ -22,5 +22,9 @@
       <li><a href="https://docs.notifications.service.gov.uk/{{ key }}.html" target="_blank" rel="noopener">{{ label }}</a></li>
     {% endfor %}
   </ul>
-    <p>You can work directly with the API, but this may be complicated to set up. <a href="{{ url_for('.feedback', ticket_type='ask-question-give-feedback') }}">Contact us</a> for more information.</p>
+    <p>A developer should be able to set up the API client and start sending test messages in around 30 minutes. A full integration might take a couple of days.</p>
+  <h2>Integrating directly with the API</h2>
+    <p>You can integrate directly with the Notify API.</p>
+    <p>To send a message you'll need to create an HTTPS request and add an authorisation header with your API key. The API key is encoded with JSON Web Tokens (JWT).</p>
+    <p>Reading the client documentation will help you to do this.</p>
 {% endblock %}