Document when matchers without a layer are matched

[abeforgit]

I assume it's either before all other layers, or after all other layers :)
Would be handy to have in the readme which one it is.

E.g.:

defmodule Dispatcher do
  use Matcher



   define_layers [ :api_services, :api, :frontend, :not_found ]

  match "/path" do
    forward conn, path, "http://foo/"
  end

  match "/path", %{ layer: :api } do
    forward conn, path, "http://bar/"
  end
end

will a request to /path be forwarded to foo, or to bar?