Remove most version specifiers in `README` (#1573) #601

Job	Run time
Pass MSRV values to other jobs	2s
format/nightly	15s
clippy/stable	16s
miri	10m 41s
cross_test/s390x-unknown-linux-gnu/stable	7m 52s
cargo-careful	1m 45s
cross_test/i686-unknown-linux-gnu/stable	2m 2s
docs/nightly	21s
nostd/thumbv6m-none-eabi/stable	16s
blas-msrv	53s
tests/stable	2m 20s
tests/nightly	2m 50s
tests/1.64.0	3m 33s
tests/beta	2m 18s
conclusion	4s
	35m 28s

Provide feedback