Add Elixir examples for recursion

03_recursion/elixir/01_countdown.exs

@@ -0,0 +1,12 @@
+defmodule Countdown do
+  defguardp non_positive?(x) when x <= 0
+
+  def from(i) when non_positive?(i), do: nil
+
+  def from(i) do
+    IO.puts(i)
+    from(i - 1)
+  end
+end
+
+Countdown.from(5)