Fix bad rust-ndarray link in README #302

Job	Run time
conda (ubuntu, conda-forge, stable)	50s
conda (windows, conda-forge, stable)	2m 36s
rustfmt	1m 38s
conda (macos, conda-forge, stable)	57s
static builds (ubuntu-latest, stable)	1m 26s
Address sanitizer	1m 21s
static builds (windows-latest, stable-msvc)	5m 48s
static builds (windows-latest, stable-gnu)	4m 44s
test apt (stable)	42s
static builds (macos-11, stable)	4m 24s
test apt (beta)	41s
static builds (macos-latest, stable)	1m 52s
test apt (nightly)	36s
	27m 35s

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