Update index.html add discord

Author: mulle-nat

index.html

@@ -140,6 +140,8 @@ <h2>+[mulle-objc install]</h2>
       <section class="keep-together">
       <h2>+[mulle-objc support]</h2>
 
+      Get support on the [mulle-objc Discord](https://discord.gg/3jUQCUgw).
+        
       Support the project by <a href="https://github.com/mulle-objc/mulle-objc.github.io/issues/1">becoming a public member</a> of <tt>mulle-objc</tt> and 
       to get a nice logo for your github profile: 
       <p>