Updating mechanism license statement in README.md

Author: Aleksandr Ovcharenko

README.md

@@ -112,6 +112,8 @@ into a file `out.#mpi_rank`. These files should be combined and sorted to compar
 ## License
 * See LICENSE.txt
 * See [NEURON](https://www.neuron.yale.edu/neuron/)
+* The mechanisms and test datasets appearing in the CoreNeuron repository are subject to the BBP license.
+  For more information please visit the [NMC portal](https://bbp.epfl.ch/nmc-portal/welcome)
 
 ## Contributors
 To facilitate the future distributions of the software the Blue Brain Project wishes to remain the sole