Add compute shader demo

[MoltenCoffee]

I've build a demo project using a compute shader for heightmap generation. It tackles both the calling of a compute shader as well as some important information on using shaders. All thoroughly commented so people can read along step by step. Furthermore it enables people to compare with CPU code and compare the performance of both options.

It is not the most simple compute shader demo imaginable, but I do feel it has the advantage of showing when a compute shader might be beneficial over CPU work, as well as give a concrete example of a use case.

Kind regards, TJ