Add docs about the new stuff #7913

Job	Run time
android	23s
cargo-deny aarch64-apple-darwin	39s
Format + check + test	5m 15s
cargo-deny aarch64-linux-android	38s
Check wasm32 + wasm-bindgen	2m 44s
cargo-deny i686-pc-windows-gnu	38s
Check Windows	1m 28s
cargo-deny i686-pc-windows-msvc	37s
cargo-deny i686-unknown-linux-gnu	40s
cargo-deny wasm32-unknown-unknown	40s
cargo-deny x86_64-apple-darwin	40s
cargo-deny x86_64-pc-windows-gnu	46s
cargo-deny x86_64-pc-windows-msvc	42s
cargo-deny x86_64-unknown-linux-gnu	40s
cargo-deny x86_64-unknown-linux-musl	42s
cargo-deny x86_64-unknown-redox	50s
	18m 2s

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