docs(readme): add nuget downloads #324

Job	Run time
Build (net8.0, 8.0.x, windows, windows, win-x64)	1m 19s
Test (net6.0, 6.0.x, windows-latest)	12m 3s
Build (net8.0, 8.0.x, macos, macos, osx-x64)	50s
Test (net6.0, 6.0.x, macos-latest)	15m 28s
Build (net8.0, 8.0.x, linux, ubuntu, linux-x64)	40s
Test (net6.0, 6.0.x, ubuntu-latest)	12m 1s
Test (net7.0, 7.0.x, windows-latest)	14m 42s
Test (net7.0, 7.0.x, macos-latest)	13m 33s
Test (net7.0, 7.0.x, ubuntu-latest)	11m 42s
Test (net8.0, 8.0.x, windows-latest)	11m 42s
Test (net8.0, 8.0.x, macos-latest)	10m 53s
Test (net8.0, 8.0.x, ubuntu-latest)	11m 10s
Release	0s
	1h 56m 3s

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