Simplify and update README for stable release #2321

Job	Run time
build (windows-latest, Debug)	11m 51s
build (windows-latest, Release)	11m 37s
build (ubuntu-latest, Debug)	7m 3s
build (ubuntu-latest, Release)	7m 10s
build (macos-latest, Debug)	4m 33s
build (macos-latest, Release)	8m 30s
publish-coverage	-1s
	50m 43s

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