docs: add NG-DE 2019 to events page (#29079)

PR Close #29079

aio/content/marketing/events.html

@@ -31,6 +31,12 @@
       <td>London, UK</td>
       <td>September 19-20, 2019</td>
     </tr>
+    <!-- NG-DE 2019-->
+    <tr>
+      <th><a href="https://ng-de.org/" title="NG-DE">NG-DE</a></th>
+      <td>Berlin, Germany</td>
+      <td>August 29th workshops, 30-31 conference, 2019</td>
+    </tr>
     </tbody>
   </table>