Added link to PyNN tutorial in HBP Collaboratory

Author: apdavison

Exercises/Exercise4_NeoPyNNJupyter.md

@@ -4,4 +4,5 @@
 This demonstration will illustrate the functionality of the multi simulator 
 model specification format [PyNN](http://neuralensemble.org/PyNN/) and the data
 storage API [Neo](http://neuralensemble.org/Neo/) through the use of browser based 
-[Jupyter notebooks](http://jupyter.org/), as can be run on [Binder](http://mybinder.org/).
+[Jupyter notebooks](http://jupyter.org/), as can be run on [Binder](http://mybinder.org/)
+or in the [HBP Collaboratory](https://collab.humanbrainproject.eu/#/collab/3833/nav/30316).