Update nuget why docs once --format option is released

[japarson]

Describe the issue or suggestion

A couple new options are being added to the nuget why command the documentation needs to be updated. The feature is currently under review and I'm not sure if it'll be backported or released in some version of .NET 10.

• Add json rendering option to nuget why command NuGet/NuGet.Client#6406
• https://learn.microsoft.com/en-us/dotnet/core/tools/dotnet-nuget-why