message: Update the README with the versions of the software we actually test with CI.
diff: @@ -20,56 +20,33 @@ Prerequisites
  -------------
  -### Linux
  +### Linux and Mac OS
  For Ginkgo core library:
  -* _cmake 3.1+_
  -* C++11 compliant compiler, one of:
  - * _gcc 5.4.0+_
  - * _clang 3.3+_ (__TODO__: verify, works with 5.0)
  -
  -The Ginkgo CUDA module has the following __additional__ requirements:
  -
  -* _cmake 3.10+_
  -* _CUDA 7.0+_ (__TODO__: verify, works with 8.0)
  -* Any host compiler restrictions your version of CUDA may impose also apply
  - here. For the newest CUDA version, this information can be found in the
  - [CUDA installation guide](http://docs.nvidia.com/cuda/cuda-installation-guide-linux/index.html#system-requirements)
  -
  -In addition, if you want to contribute code to Ginkgo, you will also need the
  -following:
  -
  -* _clang-format 5.0.1+_ (ships as part of _clang_)
  -
  -
  -### Mac OS
  -
  -For Ginkgo core library:
  -
  -* _cmake 3.1+_
  +* _cmake 3.8+_
  * C++11 compliant compiler, one of:
  - * _gcc 5.4.0+_ (__TODO__: verify)
  - * _clang 3.3+_ (__TODO__: verify)
  + * _gcc 5.5.0+_
  + * _clang 3.9+_
  * _Apple LLVM 8.0+_ (__TODO__: verify)
  The Ginkgo CUDA module has the following __additional__ requirements:
  -* _cmake 3.8+_
  -* _CUDA 7.0+_ (__TODO__: verify)
  +* _CUDA 9.0+_
  * Any host compiler restrictions your version of CUDA may impose also apply
  here. For the newest CUDA version, this information can be found in the
  - [CUDA installation guide](http://docs.nvidia.com/cuda/cuda-installation-guide-mac-os-x/index.html)
  + [CUDA installation guide for Linux](https://docs.nvidia.com/cuda/cuda-installation-guide-linux/index.html#system-requirements)
  + or [CUDA installation guide for Mac Os X](https://docs.nvidia.com/cuda/cuda-installation-guide-mac-os-x/index.html#system-requirements)
  In addition, if you want to contribute code to Ginkgo, you will also need the
  following:
  * _clang-format 5.0.1+_ (ships as part of _clang_)
  * __NOTE:__ If you want to use _clang_ as your compiler and develop Ginkgo,
  - you'll currently need two versions _clang_: _clang 4.0.0_ or older, as this
  - is this version supporetd by the CUDA 9.1 toolkit, and _clang 5.0.1_ or
  + you'll currently need two versions of _clang_: _clang 4.0.0_ or older, as
  + this is this version supported by the CUDA 9.1 toolkit, and _clang 5.0.1_ or
  newer, which will not be used for compilation, but only provide the
  - _clang-format_ utility
  + _clang-format_ utility.
  ### Windows
  