message: DOC: add warning for host/device lambdas on CPU
diff: *
  * \brief Convenience macro used for lambda capture by value.
  * \note When CUDA is used, the macro always expands to a host/device lambda.
  + *
  + * \warning When compiling with CUDA, host/device lambdas incur a significant
  + * penalty on the CPU code. The way NVCC implements host/device lambdas
  + * prevents the compiler from proper in-lining them. When CUDA is enabled use
  + * the parallel_gpu execution policy or opt to turn off CUDA if the application
  + * is making more use of the parallel_cpu and serial execution policies.
  */
  #ifdef AXOM_USE_CUDA
  #define AXOM_LAMBDA [=] AXOM_HOST_DEVICE
  