[HIPIFY][doc] Update README.md due to LLVM 9.0.0 release
[HIPIFY][doc] Update README.md due to LLVM 9.0.0 release

+ LLVM 9.0.0 is latest stable release, no patches are needed
+ The latest CUDA 10.1 Update 2 is supported
+ Tested on Windows and Linux

ROCm-Developer-Tools/HIP,ROCm-Developer-Tools/HIP,GPUOpen-ProfessionalCompute-Tools/HIP,GPUOpen-ProfessionalCompute-Tools/HIP,GPUOpen-ProfessionalCompute-Tools/HIP,ROCm-Developer-Tools/HIP,ROCm-Developer-Tools/HIP,ROCm-Developer-Tools/HIP,GPUOpen-ProfessionalCompute-Tools/HIP,GPUOpen-ProfessionalCompute-Tools/HIP