message: DOC: document fix to BVH construction on GPUs
diff: @@ -62,6 +62,10 @@ The Axom project release numbers follow [Semantic Versioning](http://semver.org/
  ex. `level_error` is now `message_error`.
  ### Fixed
  +- Fixed issue in the parallel construction of the BVH on GPUs, due to incoherent
  + L1 cache that could result in some data corruption in the BVH. The code now
  + calls ``__threadfence_system()`` after the parent is computed and stored back
  + to global memory to ensure that the *write* is visible to all threads.
  - Fixed issue in Mint that would cause the clang@9.0.0 compiler to segfault. The
  `mint_cell_types.cpp` test was causing a segfault in the compiler. The main
  issue triggering this compiler bug was the use of `constexpr` when defining the
  