README rewrite (c't style) + COMPARISON.md + AMX SIGILL fix #170

Job	Run time
Pass MSRV values to other jobs	4s
cross_test/s390x-unknown-linux-gnu/stable	1m 33s
native-backend/stable	38s
clippy/stable	23s
format/stable	19s
nostd/thumbv6m-none-eabi/stable	29s
cross_test/i686-unknown-linux-gnu/stable	1m 35s
miri	0s
docs/nightly	0s
cargo-careful	0s
tests/stable	57s
tests/beta	1m 3s
tests/1.64.0	48s
blas-msrv	57s
conclusion	0s
	8m 46s

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