chore: Nix: fix stage0-from-input

doc/make/nix.md

@@ -89,7 +89,7 @@ nix run .#HEAD-as-stage0.emacs-dev&
 ```
 To run `nix build` on the second stage outside of the second editor, use
 ```bash
-nix build .#stage0-from-input
+nix build .#stage0-from-input --override-input lean-stage0 .\?rev=$(git rev-parse HEAD)
 ```
 This setup will inadvertently change your `flake.lock` file, which you can revert when you are done.
 

flake.nix

@@ -41,7 +41,9 @@
         };
         tsandebug = tsan.override { debug = true; };
         stage0-from-input = lean-packages.override {
-          stage0 = lean-stage0.packages.${system}.lean;
+          stage0 = pkgs.writeShellScriptBin "lean" ''
+            exec ${lean-stage0.packages.${system}.lean}/bin/lean -Dinterpreter.prefer_native=false "$@"
+          '';
         };
         inherit self;
       };