Fix broken links in README.md #480

Job	Run time
Clippy (stable)	23s
Miri	1m 20s
Check (stable)	14s
Rustfmt (stable)	6s
Test Suite	3m 16s
Test Suite (stable)	1m 8s
Test Suite (--no-default-features)	3m 11s
Test Suite (ubuntu-latest)	1m 4s
Test Suite (stable, --no-default-features)	58s
Test Suite (--no-default-features --features track-caller)	3m 1s
Test Suite (windows-latest)	2m 43s
Test Suite (stable, --no-default-features --features track-caller)	1m 1s
Test Suite (--no-default-features --features auto-install)	3m 3s
Test Suite (macOS-latest)	1m 1s
Test Suite (stable, --no-default-features --features auto-install)	1m 19s
Test Suite (stable, --features pyo3)	1m 0s
Test Suite (stable, --all-features)	1m 7s
Test Suite (beta)	1m 6s
Test Suite (beta, --no-default-features)	1m 0s
Test Suite (beta, --no-default-features --features track-caller)	1m 3s
Test Suite (beta, --no-default-features --features auto-install)	59s
Test Suite (beta, --features pyo3)	1m 9s
Test Suite (beta, --all-features)	1m 11s
Test Suite (nightly)	1m 7s
Test Suite (nightly, --no-default-features)	1m 8s
Test Suite (nightly, --no-default-features --features track-caller)	1m 5s
Test Suite (nightly, --no-default-features --features auto-install)	1m 4s
Test Suite (nightly, --features pyo3)	1m 9s
Test Suite (nightly, --all-features)	1m 10s
	39m 6s

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