Merge pull request #17363 from MatrixAI/zsh-helpdir

zsh: Added HELPDIR variable for interactive shells

nixos/modules/programs/zsh/zsh.nix

@@ -116,6 +116,8 @@ in
         done
 
         ${if cfg.enableCompletion then "autoload -U compinit && compinit" else ""}
+
+        HELPDIR="${pkgs.zsh}/share/zsh/$ZSH_VERSION/help"
       '';
 
     };