refactor: use a flake for Pop!_OS

flake.nix

@@ -0,0 +1,24 @@
+# https://nix-community.github.io/home-manager/index.html#ch-nix-flakes
+{
+  inputs = {
+    home-manager.inputs.nixpkgs.follows = "nixpkgs";
+    home-manager.url = "github:nix-community/home-manager";
+    neovim-nightly.url = "github:nix-community/neovim-nightly-overlay";
+    nixpkgs.url = "github:nixos/nixpkgs/nixos-unstable";
+  };
+
+  outputs = { self, home-manager, neovim-nightly, nixpkgs, ... }:
+  let
+    overlays = [ neovim-nightly.overlay ];
+  in {
+    homeConfigurations = {
+      pop-os = home-manager.lib.homeManagerConfiguration {
+        modules = [     
+          { nixpkgs.overlays = overlays; }
+          ./home-manager/pop-os.nix
+        ];
+        pkgs = nixpkgs.legacyPackages.x86_64-linux;
+      };
+    };
+  };
+}