maintainers: add fernsehmuell

maintainers/maintainer-list.nix

···
       }
     ];
   };
+  fernsehmuell = {
+    email = "[e-mail]";
+    matrix = "@fernsehmuell:matrix.org";
+    github = "fernsehmuell";
+    githubId = 5198058;
+    name = "Udo Sauer";
+  };
   ffinkdevs = {
     email = "[e-mail]";
     github = "ffinkdevs";