maintainers: add simonkampe

maintainers/maintainer-list.nix

···
     githubId = 11135311;
     name = "Simon Chatterjee";
   };
+  simonkampe = {
+    email = "[e-mail]";
+    github = "simonkampe";
+    githubId = 254799;
+    name = "Simon Kämpe";
+  };
   simonvandel = {
     email = "[e-mail]";
     github = "simonvandel";