Add documentation on `wrap_err` vs `wrap_err_with` #311

Job	Run time
Check (stable)	17s
Clippy (stable)	26s
Miri	1m 3s
Rustfmt (stable)	16s
Test Suite	4m 27s
Test Suite (stable)	37s
Test Suite (--no-default-features)	4m 14s
Test Suite (ubuntu-latest)	35s
Test Suite (stable, --no-default-features)	35s
Test Suite (--features track-caller)	4m 19s
Test Suite (windows-latest)	1m 13s
Test Suite (stable, --features track-caller)	36s
Test Suite (--features auto-install)	4m 25s
Test Suite (macOS-latest)	57s
Test Suite (stable, --features pyo3)	36s
Test Suite (stable, --features auto-install)	40s
Test Suite (stable, --all-features)	40s
Test Suite (beta)	34s
Test Suite (beta, --no-default-features)	36s
Test Suite (beta, --features track-caller)	33s
Test Suite (beta, --features pyo3)	2m 17s
Test Suite (beta, --features auto-install)	35s
Test Suite (beta, --all-features)	37s
Test Suite (nightly)	43s
Test Suite (nightly, --no-default-features)	46s
Test Suite (nightly, --features track-caller)	46s
Test Suite (nightly, --features pyo3)	48s
Test Suite (nightly, --features auto-install)	43s
Test Suite (nightly, --all-features)	2m 24s
	37m 18s

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