Add nvim-lazy submodule and add plugin configuration.

pkgsets/nvim/lsp/nix-nil.nix

@@ -0,0 +1,26 @@
+{
+  lib,
+  config,
+  pkgs,
+  ...
+}:
+
+lib.optionalString (lib.elem "nvim::lsp::nix-nil" config.machine.pkgs) # lua
+  ''
+    lspconfig.nil_ls.setup({
+      cmd = {"${pkgs.nil}/bin/nil"},
+      settings = {
+        ['nil'] = {
+          formatting = {
+            command = { "${pkgs.nixfmt-rfc-style}/bin/nixfmt" }
+          },
+          maxMemoryMB = 4069,
+          -- nix = {
+          --   flake = {
+          --     autoEvalInputs = true
+          --   }
+          -- }
+        }
+      }
+    })
+  ''