Merge pull request practical-tutorials#81 from bobeff/tetris

Add Tetris tutorial

Author: tuvtran

README.md

@@ -69,6 +69,7 @@ To get started, simply fork this repo. Please refer to [CONTRIBUTING.md](CONTRIB
   * [Part 2](http://nicktasios.nl/posts/space-invaders-from-scratch-part-2.html)
   * [Part 3](http://nicktasios.nl/posts/space-invaders-from-scratch-part-3.html)
   * [Part 4](http://nicktasios.nl/posts/space-invaders-from-scratch-part-4.html)
+* [Tetris Tutorial in C++ Platform Independent](http://javilop.com/gamedev/tetris-tutorial-in-c-platform-independent-focused-in-game-logic-for-beginners/)
 
 ### OpenGL: