add documents

lib/openflow/actions/set_nw_ttl.ex

@@ -1,18 +1,38 @@
 defmodule Openflow.Action.SetNwTtl do
+  @moduledoc """
+  Set IP TTL
+  """
+
   defstruct(ttl: 0)
 
   alias __MODULE__
 
+  @type t :: %SetNwTtl{ttl: 0..0xFF}
+
+  @spec ofpat() :: 23
   def ofpat, do: 23
 
+  @doc """
+  Create a new set_nw_ttl action struct
+
+  ## Options:
+  - IP TTL
+
+  ```elixir
+  iex> %SetNwTtl{ttl: 64} = SetNwTtl.new(_ttl = 64)
+  ```
+  """
+  @spec new(ttl :: 0..0xFF) :: t()
   def new(ttl) do
     %SetNwTtl{ttl: ttl}
   end
 
+  @spec to_binary(t()) :: <<_::16, _::_*8>>
   def to_binary(%SetNwTtl{ttl: ttl}) do
     <<23::16, 8::16, ttl::8, 0::size(3)-unit(8)>>
   end
 
+  @spec read(<<_::16, _::_*8>>) :: t()
   def read(<<23::16, 8::16, ttl::8, _::size(3)-unit(8)>>) do
     %SetNwTtl{ttl: ttl}
   end