Initial NixOS flake-based multi-host setup

Add a NixOS system configuration using flakes, supporting multiple hosts (desktop, laptop, my-machine) with shared and per-host settings. Includes Home Manager integration, user-level and system-level package management, and example hardware configuration placeholders. Provides a README with setup instructions and a .gitignore for common Nix and editor artifacts.

README.md

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+# NixOS System Configuration
+
+This is a NixOS flake configuration for managing your system setup, ricing, and applications across multiple devices.
+
+## Structure
+
+```
+.
+├── flake.nix                    # Main flake configuration
+├── flake.lock                   # Locked dependency versions
+├── system/
+│   └── common.nix               # Shared system configuration
+├── hosts/
+│   └── my-machine/              # Per-machine configurations
+│       ├── configuration.nix    # Machine-specific settings
+│       └── hardware-configuration.nix  # Hardware-specific settings
+└── home/
+    └── home.nix                 # User-level configuration (dotfiles, packages)
+```
+
+## Initial Setup
+
+1. **Generate hardware configuration** on your NixOS machine:
+   ```bash
+   nixos-generate-config --show-hardware-config > hardware-configuration.nix
+   ```
+   Copy the output to `hosts/my-machine/hardware-configuration.nix`
+
+2. **Update configuration files**:
+   - Change `my-machine` to your actual hostname throughout the files
+   - Update `yourusername` to your actual username
+   - Adjust timezone, locale, and other personal settings
+   - Choose your desktop environment / window manager
+
+3. **Update flake inputs**:
+   ```bash
+   nix flake update
+   ```
+
+4. **Build and switch to the new configuration**:
+   ```bash
+   sudo nixos-rebuild switch --flake .#my-machine
+   ```
+
+## Adding a New Machine
+
+1. Create a new directory under `hosts/` with your machine's hostname
+2. Generate and add the hardware configuration
+3. Create a `configuration.nix` for machine-specific settings
+4. Add the new machine to `flake.nix` under `nixosConfigurations`
+5. Build with: `sudo nixos-rebuild switch --flake .#new-machine`
+
+## Updating the System
+
+```bash
+# Update flake inputs
+nix flake update
+
+# Rebuild system
+sudo nixos-rebuild switch --flake .#my-machine
+```
+
+## Customization Ideas
+
+- Add window manager configurations (i3, bspwm, Hyprland, etc.)
+- Configure terminal emulators (Alacritty, Kitty, WezTerm)
+- Set up status bars (Polybar, Waybar)
+- Add custom themes and color schemes
+- Configure rofi, dunst for notifications
+- Set up wallpaper management with nitrogen or variety
+
+## Resources
+
+- [NixOS Manual](https://nixos.org/manual/nixos/stable/)
+- [Home Manager Manual](https://nix-community.github.io/home-manager/)
+- [NixOS Wiki](https://nixos.wiki/)