modules/darwin/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/darwin/community-builder/default.nix

@@ -1,6 +1,16 @@
+{ pkgs, ... }:
 {
   imports = [
     ./packages.nix
     ./users.nix
   ];
+
+  programs.zsh = {
+    # 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
+  };
 }