adding design doc as a markdown, feedback changes to header
adding design doc as a markdown, feedback changes to header

bragadeesh/rocFFT,ROCmSoftwarePlatform/rocFFT,bragadeesh/rocFFT,ROCmSoftwarePlatform/rocFFT,tingxingdong/rocFFT-1,ROCmSoftwarePlatform/rocFFT,tingxingdong/rocFFT-1,bragadeesh/rocFFT,tingxingdong/rocFFT-1,ROCmSoftwarePlatform/rocFFT