Add coordinates for current SDV slack

This is a minimal change mentions the Slack, and invites people to join. No direkt Slack invite still goes via mail to Michael.

layouts/partials/coming-soon-header.html

@@ -48,6 +48,10 @@
         <strong>decreasing time-to-market</strong>, and sharing best practices
         and overcome the <strong>war for talent</strong>.
       </p>
+      <p>
+        To stay in contact and get relevant updates and information as things develop, 
+        we recommend you
+      </p>
     </div>
     <p class="margin-bottom-0 text-center">
       <a
@@ -56,5 +60,14 @@
         >Join the Mailing List</a
       >
     </p>
+    <p>As we are preparing to launch of the working group we are also using Slack
+        to stay in contact. We'd like to invite you there, to share your input</p>
+    <p class="margin-bottom-0 text-center">
+    <a
+      class="btn btn-primary"
+      href="mailto:michael.plagge@eclipse-foundation.org?subject=SDV%20Slack&body=Hi%20Michael,%0A%0APlease%20send%20me%20an%20invite%20to%20the%20SDV%20slack"
+    >Request access to SDV Slack</a>
+  </p>
+  </div>
   </div>
 </div>