Missing redirections

[Youssef1313]

https://docs.microsoft.com/en-us/dotnet/csharp/whats-new/csharp-7-1

This link is used in the description of this youtube video from dotNET channel. One of the comments is complaining that the link is broken. So a redirection is needed.

[BillWagner]

Thanks for noting this @Youssef1313

I've just submitted #21059 to address this.