Clarify maintenance status of the crate #307

Job	Run time
cross_compile_wasm	1m 41s
build (1.61.0, test)	3m 52s
cross_compile_aarch64 (nightly-2022-03-24)	6m 11s
build (1.61.0, benchmark)	5m 18s
cross_compile_aarch64 (nightly-2022-03-24, rayon)	6m 1s
build (1.61.0, rayon, test)	4m 28s
cross_compile_aarch64 (nightly-2022-03-24, nightly_aarch64_neon)	5m 54s
build (1.61.0, rayon, benchmark)	4m 25s
build (stable, test)	1m 15s
build (stable, benchmark)	1m 57s
build (stable, rayon, test)	1m 37s
build (stable, rayon, benchmark)	1m 57s
build (beta, test)	1m 31s
build (beta, benchmark)	2m 24s
build (beta, rayon, test)	1m 51s
build (beta, rayon, benchmark)	1m 56s
build (nightly, test)	1m 20s
build (nightly, benchmark)	2m 11s
build (nightly, rayon, test)	1m 49s
build (nightly, rayon, benchmark)	1m 54s
	59m 32s

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