Examples of Communcations Patterns in Elemental

I am not sure how to convert a local Array into `Elemental.DistMatrix`. The example in the README (and that I have used in #72 ) use `Elemental.gaussian` to fill a `DistMatrix`. However for a realistic workflow, I need to load distributed pieces of data (each local to a rank) and "fill" the `DistMatrix` locally. I seem grid objects mentioned, so there must be some way to specify which indices map to which ranks (like https://github.com/eth-cscs/ImplicitGlobalGrid.jl), but I cannot find any documentations/examples

Clearly `Elemental.gaussian!` operates locally for each rank -- e.g. if I do:
```julia
rank = MPI.Comm_rank(comm)
A = Elemental.DistMatrix(Float64);
if rank == 0
Elemental.gaussian!(A, 4000, 3200);
end
```
the program hangs.

Can you point me to the right place?