add notice about API progress and issue reporting in documentation

templates/api_v2/api_documentation.html

@@ -129,6 +129,17 @@
         </div>
     </div>
 </div>
+<div class="row">
+    <div class="col-md-12 text-right">
+        <p class="small text-muted">
+            {% trans 'This API is a work in progress and new endpoints are added as needed.' %}<br>
+            {% trans 'Missing a method or feature?' %}
+            <a target="_blank" href="https://github.com/eduardogsilva/wireguard_webadmin">
+                {% trans 'Open an issue on GitHub' %}
+            </a>
+        </p>
+    </div>
+</div>
 
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