doom: Enable magit-nix3

It shows nice status and simple navigable inspection of the flake
itself. Doesn't seem to be too taxing on performance either.

modules/emacs/doom/config.org

@@ -947,6 +947,11 @@ All the modifications that are necessary enough to exist, but not big enough to
   (add-to-list 'auto-mode-alist (cons "/flake\\.lock\\'" 'json-ts-mode))
   :config
   (add-hook 'nix-ts-mode-hook #'eglot-ensure'append))
+
+(use-package! magit-nix3
+  :after magit-status
+  :config
+  (magit-nix3-flake-mode t))
 #+end_src
 
 ** EditorConfig