Add an example how to configure it for home manager added as nixos module

[Synapsensalat]

When added as a NixOS module, the LSP doesn't work for home manager, no matter what I try in settings.json.
https://nix-community.github.io/home-manager/index.xhtml#sec-flakes-nixos-module

There are no homeConfigurations set this way

[Synapsensalat]

I found out how to edit my settings.json for home manager that's integrated as nixos module for nixd here:
https://github.com/nix-community/nixd/blob/main/nixd/docs/configuration.md

It was option B of this passage:

// Configuration examples for both approaches are shown below.
    "home-manager": {
      // A:
      "expr": "(builtins.getFlake (builtins.toString ./.)).homeConfigurations.<name>.options"

      // B:
      "expr": "(builtins.getFlake (builtins.toString ./.)).nixosConfigurations.<name>.options.home-manager.users.type.getSubOptions []"
    }

Maybe this could be added to the README

[jnoortheen]

Yes it is good to have. Kindly add it under a collapsible section