Add installation link to readme. #92

Job	Run time
build-windows	32s
build-unix-like (ubuntu-22.04, g++-12, c++20)	40s
build-unix-like (ubuntu-22.04, clang++-12, c++20)	52s
build-unix-like (ubuntu-22.04, g++-11, c++20)	35s
build-unix-like (ubuntu-22.04, g++-12, c++2b)	40s
build-unix-like (ubuntu-22.04, g++-11, c++2b)	37s
build-unix-like (ubuntu-22.04, clang++-15, c++20)	33s
build-unix-like (ubuntu-22.04, clang++-14, c++20)	29s
build-unix-like (ubuntu-24.04, clang++-18, c++20)	30s
build-unix-like (ubuntu-24.04, clang++-18, c++23)	31s
build-unix-like (ubuntu-22.04, g++-10, c++20)	33s
build-unix-like (macos-latest, clang++, c++20)	12s
build-unix-like (ubuntu-24.04, clang++-17, c++20)	41s
build-unix-like (ubuntu-24.04, g++-14, c++2b)	30s
build-unix-like (ubuntu-24.04, clang++-16, c++20)	37s
	8m 32s

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