docs: correct typos and improve help info #610

Job	Run time
lint	2m 9s
test (x86_64-unknown-linux-gnu)	7m 35s
test (x86_64-unknown-linux-musl)	6m 46s
test (aarch64-unknown-linux-gnu)	6m 41s
test (aarch64-unknown-linux-musl)	6m 44s
test (x86_64-pc-windows-msvc)	11m 7s
test (i686-pc-windows-msvc)	9m 46s
test (x86_64-apple-darwin)	11m 45s
test (aarch64-apple-darwin)	4m 51s
test (wasm32-unknown-emscripten)	3m 50s
	1h 11m 14s

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