[U] Update Nix install section

README.md

@@ -34,8 +34,7 @@ Currently, these distributions have existing packages for HyFetch:
 * Universal [Lure.sh](https://lure.sh/): `lure in hyfetch` (Thanks to [@Elara6331](https://github.com/Elara6331))
 * Arch Linux: `sudo pacman -S hyfetch` (Thanks to [@Aleksana](https://github.com/Aleksanaa) and [@Antiz96](https://github.com/Antiz96))
 * Fedora Linux: `sudo dnf install hyfetch` (packaged by [@topazus](http://github.com/topazus))
-* Nix: `nix-env -i hyfetch` (Thanks to [@YisuiDenghua](https://github.com/YisuiDenghua))
+* Nix: see the [Nix install section](#nix-install)
-* Nix Profile: `nix profile install nixpkgs#hyfetch`
 * Guix: `guix install hyfetch` (Thanks to [@WammKD](https://github.com/WammKD))
 * Slackware: `sbopkg -b hyfetch` [Slackbuild](https://slackbuilds.org/repository/15.0/desktop/hyfetch/?search=hyfetch) (Thanks to [@bittin](https://github.com/bittin) , willysr (https://github.com/willysr), jebrhansen and Urchlay)
 * Homebrew: `brew install hyfetch` (Thanks to [@catumin](https://github.com/catumin) and [@osalbahr](https://github.com/osalbahr))
@@ -58,6 +57,45 @@ cargo install hyfetch
 >
 > The PyPI package has all the dependencies bundled, so it's recommended to use that instead.
 
+### Method 4: Install using Nix {#nix-install}
+
+Hyfetch is available from the nixpkgs flake as [nixpkgs#hyfetch](https://search.nixos.org/packages?query=hyfetch&show=hyfetch).
+
+For a simple imperative install using either:
+* Nix: `nix-env -i hyfetch` (Thanks to [@YisuiDenghua](https://github.com/YisuiDenghua))
+* Nix Profile: `nix profile install nixpkgs#hyfetch`
+
+But should be installed declaratively using [`programs.hyfetch` in home-manager](https://home-manager-options.extranix.com/?query=programs.hyfetch):
+```nix
+# example config (in your home.nix)
+programs.hyfetch = {
+  enable = true;
+  settings = {
+    preset = "rainbow";
+    mode = "rgb";
+    auto_detect_light_dark = true;
+    light_dark = "dark"; #
+    lightness = 0.65; # 0.0-1.0
+    color_align = {
+      mode = "vertical"; # horizontal/vertical/roll/random0
+    };
+    backend = "fastfetch"; # neofetch/fastfetch/macchina
+    args = null;
+    distro = "nixos"; # you can use "nixos_small" too!
+    pride_month_disable = false;
+    # note that ~/ (tilde) expansion will not work </3
+    custom_ascii_path = "/home/me/my_path.txt"; 
+  };
+};  
+
+# NOTE: if `settings.backend` is fastfetch/macchina, ensure the backend is installed
+home.packages = with pkgs; [
+    fastfetch
+    # or
+    macchina
+];
+```
+
 ## Usage
 
 When you run `hyfetch` for the first time, it will prompt you to choose a color system and a preset. Just follow the prompt, and everything should work (hopefully). If something doesn't work, feel free to submit an issue!