add TU Dresden corporate design LaTeX classes

shell.nix

@@ -1,4 +1,8 @@
 with import <nixpkgs> {};
+let
+  tud-cd = callPackage ./tud-cd-latex.nix {};
+
+in
 mkShell {
   buildInputs = [
     gnumake
@@ -23,9 +27,16 @@ mkShell {
       ccicons
       biblatex
       logreq
-      koma-script;
+      koma-script
+      ;
+
+      # custom LaTeX class, see https://github.com/NixOS/nixpkgs/issues/11893#issuecomment-166834399
+      "tud-cd" = {
+        pkgs = [ tud-cd ];
+      };
     })
     biber
+    tud-cd
 
     # for instance DNS query script
     (python3.withPackages (ps: with ps; [