message: Add note about libCEED in device.hpp
diff: @@ -60,7 +60,9 @@ struct Backend
  CEED_CPU = 1 << 10,
  /** @brief [device] CEED CUDA backend working in colaboration with the
  CUDA backend. Enabled when MFEM_USE_CEED = YES and
  - MFEM_USE_CUDA = YES. */
  + MFEM_USE_CUDA = YES.
  + NOTE: The current default libCEED GPU backend (ceed-cuda) uses
  + atomics and therefore is non-deterministic! */
  CEED_CUDA = 1 << 11
  };
  