Document caveats for encodeWith #254

Job	Run time
arm (arm32v7)	6m 13s
arm (arm64v8)	3m 1s
darwin_arm (self-hosted, macOS, ARM64, 8.10.7)	11m 6s
build (ubuntu-latest, 8.6, 3.8.1.0)	6m 24s
darwin_arm (self-hosted, macOS, ARM64, 9.2.6)	6m 54s
i386	4m 2s
darwin_arm (self-hosted, macOS, ARM64, 9.4.4)	9m 24s
build (ubuntu-latest, 8.8, 3.8.1.0)	6m 36s
build (ubuntu-latest, 8.10, 3.8.1.0)	6m 3s
freebsd (self-hosted, FreeBSD, X64, 9.4.8)	2m 6s
build (ubuntu-latest, 9.0, 3.8.1.0)	5m 55s
freebsd (self-hosted, FreeBSD, X64, 9.6.4)	2m 6s
build (ubuntu-latest, 9.2, 3.8.1.0)	4m 29s
build (ubuntu-latest, 9.4, 3.8.1.0)	5m 21s
build (ubuntu-latest, 9.6, 3.8.1.0)	3m 34s
build (ubuntu-latest, 9.8, 3.8.1.0)	3m 39s
build (macos-12, 9.4, 3.8.1.0)	11m 14s
build (macos-12, 9.6, 3.8.1.0)	10m 18s
build (windows-latest, 9.4, 3.8.1.0)	16m 21s
build (windows-latest, 9.6, 3.8.1.0)	17m 45s
	2h 22m 31s

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