fix(rpc-engine-types): use proper crate name in README.md #1294

Job	Run time
doctest	54s
wasm-wasi	56s
test stable --no-default-features	1m 9s
wasm-unknown	29s
test stable	1m 12s
test stable --all-features	2m 3s
clippy	29s
test nightly --no-default-features	1m 8s
test nightly	1m 11s
test nightly --all-features	2m 3s
docs	45s
test 1.76 --no-default-features	33s
feature-checks	1m 38s
test 1.76	35s
fmt	12s
	15m 17s

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