Add Asset package creation process to docs

[Doprez]

There was a recent discovery by one of the users to get nuget packages properly working in GameStudio stride3d/stride#1834 (comment)

We should document this either as a new section or by updating https://doc.stride3d.net/latest/en/manual/nuget/create-packages.html

references:
stride3d/stride#1834
stride3d/stride-community-toolkit#193