Merge pull request #125 from donmccurdy/patch-1

Fix small typo in chapter 01.

01/README.md

@@ -7,7 +7,7 @@ In the previous chapter we described shaders as the equivalent of the Gutenberg
 
 If you already have experience making drawings with computers, you know that in that process you draw a circle, then a rectangle, a line, some triangles until you compose the image you want. That process is very similar to writing a letter or a book by hand - it is a set of instructions that do one task after another.
 
-Shaders are also a set of instructions, but the instructions are excecuted all at once for every single pixel on the screen. That means the code you write has to behave differently depending on the position of the pixel on the screen. Like a type press, your program will work as a function that receives a position and returns a color, and when it's compiled it will run extraordinarily fast.
+Shaders are also a set of instructions, but the instructions are executed all at once for every single pixel on the screen. That means the code you write has to behave differently depending on the position of the pixel on the screen. Like a type press, your program will work as a function that receives a position and returns a color, and when it's compiled it will run extraordinarily fast.
 
 ![Chinese movable type](typepress.jpg)