Updating documentation_MPI notebook to use new chunksize API
Updating documentation_MPI notebook to use new chunksize API

Note that, because the documentation and tutorials follow the releases of Parcels, this PR should only be merged after #932 is merged into master _and_  this master is released. That is also why this change is a different PR than #932

OceanPARCELS/parcels,OceanPARCELS/parcels