Update README.md + suggestions

[kmgallahan]

Rework the library description to identify this as a .NET Standard 2.0 lib, and drop the reference to .NET Core as it is now just known as ".NET".

If these changes look good I would recommend a couple of additional actions:

• Update the GitHub repo description to match.
• Update the NuGet .nuspec description element to match.
• Use the NuGet .nuspec releaseNotes element to store what you are currently putting in the description element (right now the NuGet README is showing the latest release notes instead of a project description)

https://learn.microsoft.com/en-us/nuget/release-notes/nuget-1.5#package-release-notes

https://learn.microsoft.com/en-us/nuget/reference/nuspec#releasenotes

[RandomEngy]

Thanks! Updated the GitHub repo description and the description in the .nuspec.

Though for the third one it required adding the readme, not releaseNotes.