Simplify README to quick example and pointers #4

Job	Run time
recall-regression	10s
cross-compile (x86_64-unknown-linux-gnu)	10s
cross-compile (aarch64-unknown-linux-gnu)	10s
test	21s
msrv	18s
regression	9s
docs	8s
test-arm	9s
	1m 35s

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