Update ReadMe.rst

[jjkoehorst]

A small modification in the example code. A change was made to the shader configuration but was not updated in the example code. Extra modifications has been made to make the sprite line more clear.

[paddywwoof]

Hi, I thanks for this. I won't merge it from here as this file is copied from the original in pi3d.github.com/pi3d I will change that when I get home next week. If you can face it you can git merge the documentation but you will need sphinx installed and pi3d as a sibling directory to pi3d.github.io directory. Contributions to the documentation work always welcome!