Document a list of real-life, diverse(CFOS and rabies-tracing) test datasets that allow us to evaluate correctness and performance of cellfinder

[alessandrofelder]

We would like to include some good whole-brain samples for the original cellfinder application:

• here is one from our brainmapper tutorial

[adamltyson]

Could we rename this issue? It won't mean much in a few months

[matham]

I can certainly contribute some cfos data once I got it working with cellfinder well.