Add examples for hashing with `sha256` and `blake3` #4263

Job	Run time
rustfmt	11s
Check Rust stable on ubuntu with --all-targets --no-default-features	37s
Clippy	40s
Check Rust stable on ubuntu with --all-targets	49s
no-std (stable, wasm32-unknown-unknown)	40s
Check Rust stable on ubuntu with --all-targets --all-features	54s
Test Rust stable on ubuntu with --profile test-release	5m 22s
no-std (nightly, wasm32-unknown-unknown)	53s
Check Rust nightly on ubuntu with --all-targets --no-default-features	49s
Test Rust stable on ubuntu with --profile test-release --doc	3m 2s
Test Rust nightly on windows-2022	0s
Check Rust nightly on ubuntu with --all-targets	1m 0s
Test Rust nightly on ubuntu with --profile test-release	5m 13s
Test Rust nightly on ubuntu with --profile test-release --doc	3m 37s
Check Rust nightly on ubuntu with --all-targets --all-features	2m 10s
	25m 57s

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