update installation instructions link in README #259

Job	Run time
cppcheck	7m 2s
clang-format	21s
rstcheck	21s
copyright_headers	17s
vale	37s
black	34s
flake8	26s
forbidden_types	17s
isort	15s
lychee_IGNORED	26s
mypy	35s
pydocstyle	22s
pylint	39s
unused_names	18s
sphinx-rtd	3m 16s
sphinx-conda	0s
build_linux (ubuntu-22.04, gcc, boost, optimize, warning)	14m 43s
build_linux (ubuntu-22.04, gcc, openmp, python, gsl, ltdl, boost, optimize, warning)	18m 46s
build_linux (ubuntu-22.04, gcc, mpi, python, gsl, ltdl, boost, optimize, warning)	20m 25s
build_macos (macos-latest, clang, openmp, mpi, python, gsl, ltdl, boost, hdf5, optimize, warning)	13m 40s
build_linux (ubuntu-22.04, gcc, openmp, mpi, python, gsl, ltdl, boost, hdf5, sionlib, libneurosim...	33m 47s
	1h 57m 7s

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