Add support for Nuget

[kotx]

AFAIK there is no way to add nuget packages to C# repls currently.

[ghost]

There was a post on the replit feedback board that was marked "in progress". I don't see any pull requests for it, and I think it should be a top priority feature because this would be super useful to a lot of C# programmers. I really don't think it's getting done anytime soon though.

[navteniev]

I created a pull request that adds support for C# projects using the dotnet cli #62, it would be great if you can take a look at it and let me know if it works for your projects.