Use cursor from nixpkgs-unstable

Run this before you run `nixos-rebuild switch`:

```
sudo nix-channel --add https://nixos.org/channels/nixpkgs-unstable nixpkgs-unstable
sudo nix-channel --update
```

configuration.nix

@@ -3,8 +3,9 @@
 # https://search.nixos.org/options and in the NixOS manual (`nixos-help`).
 
 { config, lib, pkgs, ... }:
-
+let
-{
+  unstable = import <nixpkgs-unstable> { config = { allowUnfree = true; }; };
+in {
   nix.settings.experimental-features = [ "nix-command" "flakes" ];
   imports =
     [ # Include the results of the hardware scan.
@@ -168,7 +169,7 @@
     file
     gnumake
     awscli2
-    code-cursor
+    unstable.code-cursor
     pavucontrol
     libnotify
     alsa-tools