docs: add `NetBSD` support to readme #94

Job	Run time
Check (x86_64-unknown-illumos)	15s
Lint	13s
Test (i686-unknown-linux-gnu)	16s
Test (i686-unknown-linux-musl)	15s
Test (x86_64-unknown-freebsd)	45s
Test (x86_64-unknown-linux-gnu)	15s
Test (x86_64-unknown-openbsd)	55s
Test (x86_64-unknown-linux-musl)	18s
Test (x86_64-unknown-netbsd)	55s
Test (armv7-unknown-linux-gnueabihf)	1m 17s
Test (aarch64-linux-android)	2m 8s
Test (mips-unknown-linux-gnu)	1m 52s
Test (i686-pc-windows-gnu)	38s
Test (i686-pc-windows-msvc)	40s
Test (x86_64-pc-windows-gnu)	41s
Test (x86_64-pc-windows-msvc)	38s
Test (x86_64-apple-darwin)	29s
	12m 30s

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