pkgs(nixvim): Enable treesitter support and enable which-key plugin

pkgs/nixvim/treesitter.nix

@@ -1,2 +1,19 @@
 {...}: {
+  plugins = {
+    treesitter = {
+      enable = true;
+      # folding = true;
+      nixvimInjections = true;
+      settings = {
+        highlight = {
+          enable = true;
+          additional_vim_regex_highlighting = true;
+        };
+        indent.enable = true;
+      };
+    };
+    which-key = {
+      enable = true;
+    };
+  };
 }