`zarr_v2_to_v3` example: clarify how V2 metadata is stored #793

Job	Run time
build_and_test_macos (macos-13)	2m 19s
clippy	36s
build_and_test_windows	2m 53s
build_and_test_macos (macos-latest)	1m 7s
build_and_test (stable, --features "")	1m 39s
build_and_test (stable, --all-features)	2m 14s
codecov	1m 33s
build_and_test (stable, --no-default-features)	1m 7s
fmt	23s
minimal-versions	38s
build_and_test (1.77, --features "")	1m 45s
build_and_test (1.77, --all-features)	2m 14s
semver	1m 45s
build_and_test (1.77, --no-default-features)	1m 7s
build_and_test (beta, --features "")	1m 34s
build_and_test (beta, --all-features)	2m 9s
build_and_test (beta, --no-default-features)	1m 4s
build_and_test (nightly, --features "")	1m 11s
build_and_test (nightly, --all-features)	2m 7s
build_and_test (nightly, --no-default-features)	51s
	30m 16s

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