Update readme.md to acknowledge the standing 2GB limitation of zip and the necessity to use the 7zip/gzip

[AKrasheninnikov]

You claim that Compress-ZipArchive overcomes the 2GB limit which is not entirely correct, as #19 proves. Please reflect and acknowledge that in the readme to manage end user expectations.

Thank you very much for the Cmdlets, anyways :)

[santisq]

Hi @AKrasheninnikov, thanks for submitting the issue, it's a fair request. Would you like to contribute to updating the readme and documentation for the cmdlet? It's worth noting this issue only happens on existing file when adding new files to it due to a .NET limitation, nothing we can do here to solve the problem.