Add an example

[aprokop]

We need to add a minimal example using BVH to run a cloud of points with a radius and print out neighbors.

[aprokop]

@JBludau Do you have an example lying around to get this started? I assume that once #6 is merged, we can make it work?

[JBludau]

The example I am working on is the bvh example we did for the st-jude. I will post it in an extra pr once #6 is finished

[aprokop]

@JBludau I put a simple example as part of #8.