Update `FuturesOrdered` docs #2301

Job	Run time
codegen	33s
cargo bench	2m 8s
cargo clippy	36s
cargo +stable build	1m 5s
cargo +beta build	1m 2s
cargo +nightly build	1m 25s
cargo +1.36 build (futures-{core, io, sink})	3m 3s
cargo doc	27s
cargo hack check --feature-powerset	3m 27s
cargo fmt	15s
cargo minimal-versions build	46s
cargo miri test	8m 12s
cargo build --target thumbv7m-none-eabi	39s
cargo test -Z sanitizer=address	4m 44s
cargo build --target thumbv6m-none-eabi	54s
cargo test -Z sanitizer=memory	3m 25s
cargo test -Z sanitizer=thread	3m 2s
cargo test (ubuntu-latest)	3m 42s
cargo +1.56 build	2m 15s
cargo test (macos-latest)	5m 12s
cargo test (windows-latest)	6m 15s
cargo test (ubuntu-latest, aarch64-unknown-linux-gnu)	5m 13s
cargo test (ubuntu-latest, armv7-unknown-linux-gnueabihf)	8m 16s
cargo test (ubuntu-latest, armv5te-unknown-linux-gnueabi)	10m 21s
cargo test (ubuntu-latest, i686-unknown-linux-gnu)	4m 8s
	1h 21m 5s

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