Updates readme around .net versions supported

[Kritner]

Description

Update readme for other .net versions supported

Fixes # (issue number)

Type of Change

Use an x in between the [ ] for each line applicable to the type of change for this PR

• Bug fix
• New Feature
• Documentation
• Code improvement
• Breaking change - if a public API changes, or any change that DOES or MAY require a major revision to the NuGet package version due to semver.
• Unit tests
• Code samples
• Added your repository URL to the readme because you make use of this super cool package! ;)
• Other

Checklist

• Read the https://github.com/OrleansContrib/Orleans.SyncWork/blob/main/CONTRIBUTING.md
• Ran unit tests and ensured they passed
• Added unit tests where applicable
• Referenced an issue where applicable
• Ran dotnet-format locally