message: docs: add NG-DE 2019 to events page
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diff: <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>
  