modules/nixos/community-builder: add a sane zsh config

Biggest benefits are better prompt and the ability to properly use arrow up
to go through the history

`nix<up>` searches through commands which start with `nix`

https://grml.org/

modules/nixos/community-builder/default.nix

@@ -8,5 +8,13 @@
   # disable generated completion
   environment.etc."fish/generated_completions".text = pkgs.lib.mkForce "";
 
-  programs.zsh.enable = true;
+  programs.zsh = {
+    enable = true;
+    # https://grml.org/zsh/grmlzshrc.html
+    # https://grml.org/zsh/grml-zsh-refcard.pdf
+    interactiveShellInit = ''
+      source ${pkgs.grml-zsh-config}/etc/zsh/zshrc
+    '';
+    promptInit = ""; # otherwise it'll override the grml prompt
+  };
 }