add documents

lib/openflow/actions/group.ex

@@ -1,18 +1,38 @@
 defmodule Openflow.Action.Group do
+  @moduledoc """
+  Apply Group
+  """
+
   defstruct(id: 0)
 
   alias __MODULE__
 
+  @type t :: %Group{id: 0..0xFFFFFFFF}
+
+  @spec ofpat() :: 22
   def ofpat, do: 22
 
+  @doc """
+  Create a new group action struct
+
+  ## Options
+  - id: Group identifier
+
+  ```elixir
+  iex> %Group{id: 10} = Group.new(10)
+  ```
+  """
+  @spec new(0..0xFFFFFFFF) :: t()
   def new(id) do
     %Group{id: id}
   end
 
+  @spec to_binary(t()) :: <<_::16, _::_*8>>
   def to_binary(%Group{id: id}) do
     <<22::16, 8::16, id::32>>
   end
 
+  @spec read(<<_::16, _::_*8>>) :: t()
   def read(<<22::16, 8::16, id::32>>) do
     %Group{id: id}
   end