Instances counter in documentation?

[UlrikeS91]

I think it would be nice to have a "current count" for all instances in the openMINDS_instances repo somewhere in the docu. The development of these instances is a huge effort and users could benefit from getting a rough estimate of how much there actually is. It's hard to get this overview without doing some work. I had to write a small script to get these numbers and realized that we have almost 15.000 instances which is quite a number 😉

[lzehl]

@Raphael-Gazzotti I think this is a nice idea that we can incorporate into the docu. @apdavison we should also include this in the instances stats that you started (I think we still need to link this effort onto the README in openMINDS_instances).