Add instructions for sdl2 install to readme

Author: David Voswinkel

README.md

@@ -5,18 +5,23 @@ vecx
 
 Requirements
 ------------
-* `libsdl`
-* `sdl_gfx`
-* `sdl_image`
+* `libsdl2`
+* `sdl2_gfx`
+* `sdl2_image`
+
+```brew install  sdl2  sdl2_gfx sdl2_image```
 
 Usage
 -----
 
+```vecx game.bin```
+
 Authors
 -------
 
 * Valavan Manohararajah - original author
 * [John Hawthorn](https://twitter.com/jhawthorn) - SDL port
 * [Nikita Zimin](https://twitter.com/nzeemin) - audio
+* [Optixx](https://twitter.com/optixx) - SDL2 port