message: Advertise HIP in the README.md.
diff: @@ -51,6 +51,12 @@ following:
  * _clang-tidy_ (optional, when setting the flag `-DGINKGO_WITH_CLANG_TIDY=ON`)
  * _iwyu_ (Include What You Use, optional, when setting the flag `-DGINKGO_WITH_IWYU=ON`)
  +The Ginkgo HIP module has the following __additional__ requirements:
  +
  +* the HIP, hipBLAS and hipSPARSE packages compiled with either:
  + * _AMD_ backend
  + * _CUDA 9.0+_ backend. When using CUDA 10+ _cmake 3.12.2+_ is required.
  +
  ### Windows
  The prequirement needs to be verified
  