Move attribute and license info to readme.

README.md

@@ -256,3 +256,5 @@ Many examples use creative commons or public domain artwork for illustrative pur
 * DDS test images (alpine_cliff_a, alpine_cliff_a_norm, alpine_cliff_a_spec) taken from the CC0 license [0-AD texture pack by Wildfire games](http://opengameart.org/content/0-ad-textures)
 * Tile set for tile mapping demo (tiles.png) from CC0 licensed [cobblestone paths pack](http://opengameart.org/content/rpg-tiles-cobble-stone-paths-town-objects)
 * Audio track for `audio.js` example is "[Bamboo Cactus](https://archive.org/details/8bp033)" by [8bitpeoples](https://archive.org/details/8bitpeoples).  CC BY-ND-NC 1.0 license
+* Matcap (spheretexture.jpg) by [Ben Simonds](https://bensimonds.com/2010/07/30/matcap-generator/). CC 3 license.
+* Normal map (normaltexture.jpg) by [rubberduck](http://opengameart.org/node/21219). CC0 license.

example/metaball.js

@@ -275,7 +275,6 @@ require('resl')({
   manifest: {
     sphereTexture: {
       type: 'image',
-      // sphere texture from https://bensimonds.com/2010/07/30/matcap-generator/
       src: 'assets/spheretexture.jpg',
       parser: (data) => regl.texture({
         data: data,
@@ -285,7 +284,6 @@ require('resl')({
     },
     normalTexture: {
       type: 'image',
-      // normal texture from http://opengameart.org/node/21219
       src: 'assets/normaltexture.jpg',
       parser: (data) => regl.texture({
         data: data,