Update README.md with another one C# implementation

[cbuctok]

It is actually based on UUIDv7 so it is sortable. Right now it is WIP of course.

[loreto]

@cbuctok Thanks for contributing.

Happy to add it, due to a quirk of our internal setup, I need to accept the PR in our opensource monorepo and then it'll automatically get published here. Do you mind opening the PR there? The corresponding file is here: https://github.com/jetpack-io/opensource/blob/main/typeid/typeid/README.md

Once you're ready to validate the implementation, I've added two files with test data to the spec: https://github.com/jetpack-io/typeid/blob/main/spec/valid.yml and https://github.com/jetpack-io/typeid/blob/main/spec/invalid.yml. Once you write unit tests showing that your implementation passes tests based on that data, and we can mark it as validated.

[cbuctok]

Closing pull request, moved to https://github.com/jetpack-io/opensource/pull/64