add mix bootstrap function

nt/primitives/mix/bootstrap.nix

@@ -0,0 +1,10 @@
+# WARNING: This file is strictly for bootstrapping nt
+rec {
+  # NOTE: bootstrap does the equivalent to mix's `include.public` option.
+  # NOTE: It also provides itself as input to descendents.
+  bootstrap = args: paths: let
+    input = args // {inherit this bootstrap;};
+    this = paths |> builtins.foldl' (acc: el: acc // import el input) {};
+  in
+    this;
+}