docs: Add documents for openflow actions

lib/openflow/actions/push_vlan.ex

@@ -1,18 +1,39 @@
 defmodule Openflow.Action.PushVlan do
+  @moduledoc """
+  Push a new VLAN tag
+
+      send_flow_mod_add(
+        datapath_id,
+        instructions: ApplyActions.new(PushVlan.new())
+      )
+  """
+
   defstruct(ethertype: 0x8100)
 
   alias __MODULE__
+  @type t :: %PushVlan{ethertype: 0..0xFFFF}
 
+  @spec ofpat() :: 17
   def ofpat, do: 17
 
+  @doc """
+  Create a new push_vlan action struct.\\
+  0x8100 is a default value.
+
+      iex> %PushVlan{ethertype: 0x8100} = PushVlan.new()
+  """
+  @spec new() :: t()
+  @spec new(ethertype :: 0..0xFFFF) :: t()
   def new(ethertype \\ 0x8100) do
     %PushVlan{ethertype: ethertype}
   end
 
+  @spec to_binary(t()) :: <<_::16, _::_*8>>
   def to_binary(%PushVlan{ethertype: ethertype}) do
     <<17::16, 8::16, ethertype::16, 0::size(2)-unit(8)>>
   end
 
+  @spec read(<<_::16, _::_*8>>) :: t()
   def read(<<17::16, 8::16, ethertype::16, 0::size(2)-unit(8)>>) do
     %PushVlan{ethertype: ethertype}
   end