Enable host toolchain on macOS by default, improve `README.md` #33

Job	Run time
Test / Linux (5.8 - jammy)	2m 56s
Test / Linux (5.9 - jammy)	3m 6s
Test / Linux (5.10 - jammy)	3m 11s
Test / Windows (${{ matrix.swift_version }} - ${{ ((inputs.enable_windows_docker && contains(matrix.swift_version, 'nightly') && 'windows-2019') \|\| 'windows-2022') }})	0s
Test / Linux (6.0 - jammy)	3m 24s
Test / Linux (nightly-main - jammy)	4m 1s
Test / Linux (nightly-6.1 - jammy)	4m 6s
Soundness / Unacceptable language check	3s
Soundness / API breakage check	0s
Soundness / Documentation check	33s
Soundness / Broken symlinks check	3s
Soundness / Format check	32s
Soundness / License headers check	4s
Soundness / Shell check	30s
Soundness / Python lint check	4s
Soundness / YAML lint check	3s
	22m 36s

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