add a basic nixvim config

nixos/nvim.nix

@@ -1,7 +1,18 @@
-{
+{ pkgs, ... }: {
   programs.nixvim = {
+    extraPackages = with pkgs; [ fd ];
     enable = true;
     viAlias = true;
     vimAlias = true;
+    colorschemes.catppuccin.enable = true;
+    plugins = {
+      conform-nvim = {
+        enable = true;
+      };
+      treesitter.enable = true;
+      cmp.enable = true;
+      cmp-nvim-lsp.enable = true;
+      lsp.enable = true;
+    };
   };
 }