Add more shader learning resources

Author: hughsk

index.html

@@ -66,10 +66,12 @@ <h3>WebGL Workshop</h3>
       <p>
         Some other good learning resources include
         <a target="_blank" href="http://learningwebgl.com">Learning WebGL</a>,
-        <a target="_blank" href="http://www.webglacademy.com/">WebGL Academy</a>, and
+        <a target="_blank" href="http://www.webglacademy.com/">WebGL Academy</a>,
+        <a target="_blank" href="http://shadertoy.com">Shadertoy</a>, and
         <a target="_blank" href="http://glslsandbox.com/">GLSL Sandbox</a>.
 
         If you're particularly interested in shaders, you might want to check out
+        <a target="_blank" href="http://thebookofshaders.com">The Book of Shaders</a>,
         <a target="_blank" href="http://aerotwist.com/tutorials/an-introduction-to-shaders-part-1/">An Introduction to Shaders</a> or
         <a target="_blank" href="http://notes.underscorediscovery.com/shaders-a-primer/">Primer: Shaders</a>.
       </p>