doc: added comments and updated to latest ashautentication version and required changes

lib/mv_web/live_user_auth.ex

@@ -11,10 +11,12 @@ defmodule MvWeb.LiveUserAuth do
   # on_mount {MvWeb.LiveUserAuth, :current_user}
   def on_mount(:current_user, _params, session, socket) do
     return_to = session[:return_to]
+
     socket =
       socket
       |> assign(:return_to, return_to)
       |> AshAuthentication.Phoenix.LiveSession.assign_new_resources(session)
+
     {:cont, session, socket}
   end