add mastodon link

Author: gluap

content/_index.de.html

@@ -35,6 +35,10 @@ <h2 class="display-4 mb-3">Überholabstandsmessung für Radfahrende</h2>
 	<a class="btn btn-lg btn-secondary me-3 mb-4" href="#unterstuetzen" rel="noopener noreferrer nofollow">
 		<i class="fas fa-hand-holding-heart me-1"></i> Unterstützen
 	</a>
+
+	<a class="btn btn-lg btn-secondary me-3 mb-4" href="https://verkehrswende.social/@OpenBikeSensor" target="_blank" rel="me noopener noreferrer nofollow">
+		<i class="fab fa-mastodon me-1"></i> Mastodon
+	</a>
 </div>
 </div>
 {{< /blocks/cover >}}