integrate subtle-ads via api instead of submodule

_includes/subtle-ads/subtle-ads.html

@@ -0,0 +1,20 @@
+<script src="https://unpkg.com/[email protected]"
+        integrity="sha384-FhXw7b6AlE/jyjlZH5iHa/tTe9EpJ1Y55RjcgPbjeWMskSxZt1v9qkxLJWNJaGni"
+        crossorigin="anonymous"></script>
+
+<div hx-get="https://arc42-subtle-ads-backend.vercel.app/api"
+     hx-trigger="load delay"
+     hx-swap="outerHTML"
+     hx-target="#subtle-ads">
+</div>
+
+<div id="subtle-ads">
+    <h4>arc42 offers architecture training.</h4>
+    <p>
+        The data is currently loaded from the backend and should display here shortly.
+        If not, you can see the next dates at
+        <a rel="noopener noreferrer nofollow" target="_blank" href="https://dates.arc42.org">
+            dates.arc42.org
+        </a>.
+    </p>
+</div>