docs: note about rosetta install on mac

Author: srid

doc/start/nix.md

@@ -11,13 +11,15 @@ This installer automatically [enable flakes](https://nixos.wiki/wiki/Flakes#Enab
 To test your Nix install, run:
 
 ```sh
-nix run nixpkgs#hello
+nix run nixpkgs#nix-info -- -m
 ```
 
+Note: If you are on an ARM-based Mac (like M1), the `system` field of `nix-info`'s output must say `"aarch64-darwin"`. If it instead says `"x86_64-darwin"`, it means that you have incorrectly installed Nix (i.e., under Rosetta).
+
 ## See also
 
 - [[nix-rapid]]
 - [NixOS](https://nixos.org/), a Linux distro based on the Nix package manager.
 - [nix-darwin](https://github.com/LnL7/nix-darwin), replaces homebrew and the like on macOS, using Nix.
 
-[^so]: Use the `sysctl -n sysctl.proc_translated` command to check this. [Ref](https://stackoverflow.com/a/67690510/55246)
+[^so]: Use the `sysctl -n sysctl.proc_translated` command to check this. [Ref](https://stackoverflow.com/a/67690510/55246)