Add multilingual Agila learning examples and Git practice guide

en/ada-functions-and-packages/main.adb

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+with Ada.Text_IO;
+
+procedure Main is
+   function Remaining (Total, Done : Natural) return Natural is
+   begin
+      if Done >= Total then
+         return 0;
+      end if;
+      return Total - Done;
+   end Remaining;
+begin
+   Ada.Text_IO.Put_Line (Natural'Image (Remaining (4, 1)));
+end Main;