Add news regarding current maintenance state

app/templates/main/news.html.j2

@@ -8,6 +8,22 @@
       <h1 id="title">{{ title }}</h1>
     </div>
 
+    <div class="col s12">
+      <div class="card" id="maintenance">
+        <div class="card-content">
+          <span class="card-title">Maintenance</span>
+          <p>Dear users</p>
+          <br>
+          <p>Currently we are rewriting big parts of our project infrastructure. Due to this the following features are not available:</p>
+          <ul>
+            <li>Corpus export and import</li>
+            <li>Query result export, import and view</li>
+          </ul>
+          <p>We hope to add these features back in the near future, until then check out our updated corpus analysis.</p>
+        </div>
+      </div>
+    </div>
+
     <div class="col s12">
       <div class="card" id="nlp-removed-language-support">
         <div class="card-content">