heading level and doc for masonry readme #2367

Job	Run time
cargo check (msrv) (windows-latest)	1m 48s
cargo check (aarch64-android)	20s
cargo check (msrv) (wasm32)	23s
cargo check (msrv) (macos-latest)	35s
cargo clippy (windows-latest)	4m 53s
cargo check (msrv) (ubuntu-latest)	41s
cargo clippy (macos-latest)	2m 10s
cargo clippy (wasm32)	1m 58s
cargo clippy (ubuntu-latest)	3m 15s
cargo doc	1m 56s
formatting	32s
Prime LFS Cache	7s
cargo test (wasm32)	20s
typos	3s
cargo test (windows-latest)	3m 40s
cargo test (macos-latest)	1m 57s
cargo test (ubuntu-latest)	4m 42s
	29m 20s

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