Update README.md to reflect Windows gnu target support #712

Job	Run time
Build Docker Image	21m 15s
linux (x86_64-unknown-linux-musl, x86_64-musl)	1m 20s
windows (x64, x86_64-pc-windows-msvc)	2m 42s
linux (i686-unknown-linux-musl, i686-musl)	1m 5s
windows (x86, i686-pc-windows-msvc)	2m 59s
linux (aarch64-unknown-linux-musl, aarch64-musl)	1m 10s
windows (arm64, aarch64-pc-windows-msvc)	4m 47s
linux (armv7-unknown-linux-musleabihf, armv7-musleabihf)	1m 16s
linux (armv7-unknown-linux-musleabi, armv7-musleabi)	1m 15s
macos	1m 17s
Release	0s
	39m 6s

Provide feedback