Improve progress bar

This improves progress bar by:
- Adding progress percentage
- Calculating progress bar underline based on the text length of progress bar

lib/display/progress_bar.ex

@@ -4,14 +4,19 @@ defmodule Display.ProgressBar do
 
   def progress_bar(%{current: current, total: total}) do
     arrow = calculate_progress(current, total) |> build_arrow
+    progress_percentage = calculate_percentage(current, total)
 
-    "|" <> String.pad_trailing(arrow, @progress_bar_length) <> "| #{current} of #{total}"
+    "|" <> String.pad_trailing(arrow, @progress_bar_length) <> "| #{current} of #{total} -> #{progress_percentage}% complete"
   end
 
   defp calculate_progress(current, total) do
     round(current / total * @progress_bar_length)
   end
 
+  defp calculate_percentage(current, total) do
+    Float.round(current / total * 100, 1)
+  end
+
   defp build_arrow(0), do: ""
 
   defp build_arrow(length) do