Parallelization docs should mention specific versions of P4est/T8code

When building P4est/T8code against system MPI, we should probably suggest building the specific versions of each library which are built by Yggdrasil. We ran into some issues related to the C/C++ interface being inconsistent with the interfaces used by T8code.jl.

No documentation file, test, or entry point is identified in the issue. Locate the parallelization and build documentation, then verify which P4est/T8code versions Yggdrasil builds; done means the system-MPI guidance names those versions and addresses the reported C/C++ interface compatibility concern.

Written by the indexing model from the issue text.