feat: add comprehensive NixOS configuration documentation and structure

- Introduced `08-structure.md` detailing project structure, main files, and versioning.
- Created `README.md` for documentation overview and quick start guide.
- Added user-specific configurations for Alacritty, Vim, Micro, Git, Zsh, Tmux, and tools.
- Implemented system modules for desktop environment (KDE Plasma), audio (PipeWire), networking, and services (OpenSSH, GnuPG).
- Configured Nix settings with flakes support and garbage collection.
- Established user management for `ada` with necessary groups and shell settings.
- Enabled VirtualBox guest additions for improved VM experience.

nixos/modules/users/ada.nix

@@ -0,0 +1,14 @@
+{ pkgs, ... }:
+
+{
+  # Определение учётной записи пользователя
+  users.users.ada = {
+    isNormalUser = true;
+    description = "ada";
+    extraGroups = [ "networkmanager" "wheel" ];
+    shell = pkgs.zsh;
+  };
+
+  # Включение ZSH системно
+  programs.zsh.enable = true;
+}