docs: Add a more verbose example on adding the standalone flake (nix-…

…community#1323)

docs/user-guide/install.md

@@ -74,3 +74,14 @@ There are also some helper functions in `<nixvim>.lib.${system}` like:
 The nixvim derivation can then be used like any other package!
 
 For more information you can look at the [nixvim standalone flake template](https://github.com/nix-community/nixvim/blob/main/templates/simple/flake.nix).
+
+Here is an example on how to integrate into a NixOS or Home-manager configuration when using flake parts (assuming your standalone flake's input is `nixvim-config`):
+```nix
+{ inputs, system, ... }:
+{
+  # NixOS
+  environment.systemPackages = [ inputs.nixvim-config.packages.${system}.default ];
+  # home-manager
+  home.packages = [ inputs.nixvim-config.packages.${system}.default ];
+}
+```