Merge pull request #69 from mkstoyanov/doc_fixups #163

Job	Run time
heffte (cmake, BUILTIN, cpu_intel)	1m 11s
heffte (cmake, FFTW, cpu_intel)	2m 7s
heffte (cmake, MKL, cpu_intel)	1m 44s
heffte (spack, BUILTIN, cpu_intel)	12m 0s
heffte (spack, FFTW, cpu_intel)	22m 26s
heffte (spack, MKL, cpu_intel)	12m 8s
heffte (cmake, ONEAPI, gpu_intel)	1m 33s
heffte (cmake, CUDA, gpu_nvidia)	6m 31s
heffte (spack, CUDA, gpu_nvidia)	17m 30s
heffte (cmake, ROCM, gpu_amd)	40s
	1h 17m 50s

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