docs: document configuring Standalone Nixvim

docs/src/configuration.md

@@ -200,6 +200,35 @@ to customize this.
 > Similarly, [`stylix.override`](options/nixos.md#stylixoverride) is not inherited
 > if the color scheme is different.
 
+## Standalone Nixvim
+
+When using a NixOS or home-manager installation of [Nixvim], you can use Stylix
+as normal. However, when using Nixvim's ["standalone" configuration mode][Nixvim Standalone],
+you will need to pass Stylix's generated config to Nixvim yourself.
+
+The generated config can be accessed as `config.lib.stylix.nixvim.config`. You
+can use this as a module in your standalone Nixvim Configuration or an
+extension of it.
+
+For example:
+
+```nix
+{ inputs, config, pkgs, ... }:
+let
+  inherit (pkgs.stdenv.hostPlatform) system;
+  nixvim-package = inputs.nixvim-config.packages.${system}.default;
+  extended-nixvim = nixvim-package.extend config.lib.stylix.nixvim.config;
+in
+{
+  environment.systemPackages = [
+    extended-nixvim
+  ];
+}
+```
+
+[Nixvim]: https://nix-community.github.io/nixvim
+[Nixvim Standalone]: https://nix-community.github.io/nixvim/user-guide/install.html#standalone-usage
+
 ## Turning targets on and off
 
 In Stylix terms, a target is anything which can have colors, fonts or a