replaced discord invite with invite to our own chat

index.html

@@ -229,7 +229,7 @@
       The community is based on <b>European standards</b>, <b>the whole world is invited</b> to collaborate.<br>
       It is registered and hosted at <a href="https://www.manitu.de/" target="_blank"><b>Manitu</b></a>, a web host service based in <b>St. Wendel, Saarland, Germany</b>.<br><br>
       <b>We'd love to hear from you!</b>
-      <h3><a href="https://discord.gg/nGDYYKE">Discord invitation</a></h3><br>
+      <h3><a href="https://coalmedia.eu/cloud/index.php/call/iw744jq5">Invitation to the chat</a></h3><br>
     </p>
     <p>
       There's a <a href="http://coal.ddns.net:3000/ember/coalmedia.eu">git-repository</a> for this website.<br>

mobile.html

@@ -67,7 +67,7 @@
       The community is based on <b>European standards</b>, <b>the whole world is invited</b> to collaborate.<br>
       It is registered and hosted at <a href="https://www.manitu.de/" target="_blank"><b>Manitu</b></a>, a web host service based in <b>Saarland, Germany</b>.<br><br>
       <b>We'd love to hear from you!</b><br><br>
-      <center><h3><a href="https://discord.gg/nGDYYKE">Discord invitation</a></h3></center>
+      <center><h3><a href="https://coalmedia.eu/cloud/index.php/call/iw744jq5">Invitation to the chat</a></h3></center>
     </p>
     <h3>Impressum</h3>
     <p>