add(flake): Add basic flake file.

flake.nix

@@ -0,0 +1,36 @@
+{
+  description = "My NixOS Configurations Flake";
+
+  inputs = {
+    # Source: https://github.com/NixOS/nixpkgs
+    nixpkgs.url = "github:nixos/nixpkgs/nixpkgs-unstable";
+    nixpkgs-old.url = "github:nixos/nixpkgs/nixos-24.11";
+    nixpkgs-latest.url = "github:nixos/nixpkgs";
+
+    # Source: https://github.com/nix-community/home-manager
+    home-manager = {
+      url = "github:nix-community/home-manager";
+      inputs.nixpkgs.follows = "nixpkgs";
+    };
+
+    # Source: https://github.com/NixOS/nixos-hardware
+    nixos-hardware.url = "github:nixos/nixos-hardware";
+
+    # Source: https://github.com/Mic92/sops-nix
+    sops-nix.url = "github:mic92/sops-nix";
+  };
+
+  outputs =
+    {
+      nixpkgs,
+      nixpkgs-old,
+      nixpkgs-latest,
+      ...
+    }@inputs:
+    let
+      #
+    in
+    {
+      #
+    };
+}