Add function in fish to quickly make a nix .envrc

fish.nix

@@ -79,6 +79,10 @@
         echo -n -s (set_color $color_cwd) (prompt_pwd) $normal (fish_vcs_prompt) \
         (set_color -i yellow) $direnv_status $normal " "$prompt_status " "$suffix " "
       '';
+      # run $argv when a file tracked by git is updated.
+      gitentr.body = ''
+        ${pkgs.git}/bin/git ls-tree -r HEAD --name-only | ${pkgs.entr}/bin/entr $argv
+      '';
     };
 
     shellAliases = {