Add mention of the image anchor affecting rotation in the sprite rotation property.
Add mention of the image anchor affecting rotation in the sprite rotation
property.

seeminglee/pyglet64,adamlwgriffiths/Pyglet,seeminglee/pyglet64,niklaskorz/pyglet,adamlwgriffiths/Pyglet,niklaskorz/pyglet,niklaskorz/pyglet,seeminglee/pyglet64,adamlwgriffiths/Pyglet,adamlwgriffiths/Pyglet,niklaskorz/pyglet