improve documentation #1656

Job	Run time
build (g++-8, Debug, 17, ubuntu-22.04, ON)	6m 56s
build (g++-8, Release, 17, ubuntu-22.04, ON)	9m 16s
build (g++-10, Debug, 17, ubuntu-22.04, ON)	6m 50s
build (g++-10, Release, 17, ubuntu-22.04, ON)	10m 15s
build (g++-13, Release, 23, ubuntu-22.04, ON, sudo apt -o Acquire::Retries=5 install g++-13)	12m 48s
build (g++-13, Debug, 23, ubuntu-22.04, ON, sudo apt -o Acquire::Retries=5 install g++-13)	8m 43s
build (g++-10, Release, 17, ubuntu-22.04, OFF, -DQUILL_NO_EXCEPTIONS=ON -DQUILL_BUILD_TESTS=ON)	2m 3s
build (g++-10, Release, 20, ubuntu-22.04, ON, -DQUILL_USE_VALGRIND=ON, -T memcheck, sudo apt -o A...	20m 18s
build (clang++-14, Release, 20, ubuntu-22.04, ON, -DQUILL_SANITIZE_ADDRESS=ON)	23m 40s
build (clang++-14, Release, 20, ubuntu-22.04, ON, -DQUILL_SANITIZE_THREAD=ON)	15m 53s
build (clang++-19, Release, 17, ubuntu-22.04, ON, wget -O - https://apt.llvm.org/llvm-snapshot.gp...	11m 10s
	2h 7m 52s

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