Add maintenance page (#239)

support/maintenance.html

@@ -0,0 +1,18 @@
+---
+layout: page
+title: Maintenance
+---
+
+<section class="publication-layout">
+  <div class="markdown-container max-w-5xl">
+    <h1 class="font-extrabold">
+      Maintenance In Progress
+    </h1>
+    <p style="margin-top: 50px;">
+      You have been redirected to here because the service you are trying to access is currently under maintenance.
+    </p>
+    <p>
+      It will be available again shortly.
+    </p>
+  </div>
+</section>