Add .NET Core 3 Support to:
on https://docs.couchbase.com/dotnet-sdk/3.0/project-docs/compatibility.html#net-framework-version-compatibility
as well as https://docs.couchbase.com/dotnet-sdk/3.0/hello-world/start-using-sdk.html#installing-the-sdk
and https://docs.couchbase.com/dotnet-sdk/3.0/project-docs/sdk-release-notes.html#installation