implement a bunch of utility functions on tun device primitive

native/p2pchat_transport_prim_tun/README.md

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+# NIF for P2pChat.Transport.TunTapPort
+
+## To build the NIF module:
+
+- Your NIF will now build along with your project.
+
+## To load the NIF:
+
+```elixir
+defmodule P2pChat.Transport.TunTapPort do
+  use Rustler, otp_app: :p2p_chat, crate: "p2pchat_transport_tuntapport"
+
+  # When your NIF is loaded, it will override this function.
+  def add(_a, _b), do: :erlang.nif_error(:nif_not_loaded)
+end
+```
+
+## Examples
+
+[This](https://github.com/rusterlium/NifIo) is a complete example of a NIF written in Rust.