Add "Computer Graphics from scratch". (#2649)

free-programming-books.md

@@ -235,6 +235,7 @@
 ### Graphics Programming
 
 * [Blender 3D: Noob to Pro](https://en.wikibooks.org/wiki/Blender_3D%3A_Noob_to_Pro)
+* [Computer Graphics from scratch](http://gabrielgambetta.com/computer-graphics-from-scratch) - Gabriel Gambetta (:construction: *in process*)
 * [DirectX manual](http://user.xmission.com/~legalize/book/download/index.html) (draft)
 * [GPU Gems](https://developer.nvidia.com/gpugems/GPUGems/gpugems_pref01.html)
 * [Graphics Programming Black Book](http://www.gamedev.net/page/resources/_/technical/graphics-programming-and-theory/graphics-programming-black-book-r1698) - Michael Abrash