Update README.md

Thank you for considering our upcoming book for the resource list.  My kids are writing it for Manning, and they're so excited to teach other kids how to code.

README.md

@@ -354,6 +354,7 @@ Must see
 * [Game Programming Gems](http://www.amazon.com/Game-Programming-Gems-CD/dp/1584500492)
 * [Game Programming Patterns](http://gameprogrammingpatterns.com/)
 * [Game Scripting Mastery](http://www.amazon.com/Scripting-Mastery-Premier-Press-Development/dp/1931841578)
+* [Hello Scratch: Learn to Program by Making Arcade Games](https://www.manning.com/books/hello-scratch)
 * [Interactive Computer Graphics: A Top-Down Approach with Shader-Based OpenGL, 6/E](http://www.pearsonhighered.com/educator/product/Interactive-Computer-Graphics-A-TopDown-Approach-with-ShaderBased-OpenGL/9780132545235.page)
 * [Level Up!](http://www.amazon.com/dp/047068867X?tag=game-prog-books-20)
 * [Mathematics For 3D Game Programming And Computer Graphics](http://www.amazon.com/dp/1435458869?tag=game-prog-books-20)