Improve docs for 'When Handler Isn't Enough'

Fixes #118

lib/thousand_island/handler.ex

@@ -156,11 +156,14 @@ defmodule ThousandIsland.Handler do
   consisting of the configured handler and genserver opts. This function is expected to return a
   conventional `GenServer.on_start()` style tuple. Note that this newly created process is not
   passed the connection socket immediately.
-  2. The socket will be passed to the new process via a message of the form
-  `{:thousand_island_ready, socket, server_config, acceptor_span, start_time}`.
-  3. Once the process receives the socket, it must call `ThousandIsland.Socket.handshake/1` with the socket as the sole
-  argument in order to finalize the setup of the socket.
-  4. The socket is now ready to use.
+  2. The raw `t:ThousandIsland.Transport.socket()` socket will be passed to the new process via a
+  message of the form `{:thousand_island_ready, raw_socket, server_config, acceptor_span,
+  start_time}`.
+  3. Your implenentation must turn this into a `to:ThousandIsland.Socket.t()` socket by using the
+  `ThousandIsland.Socket.new/3` call.
+  4. Your implementation must then call `ThousandIsland.Socket.handshake/1` with the socket as the
+  sole argument in order to finalize the setup of the socket.
+  5. The socket is now ready to use.
 
   In addition to this process, there are several other considerations to be aware of: