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 https://github.com/stride3d/stride/issues/1834#issuecomment-2591263440

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

references: https://github.com/stride3d/stride/issues/1834 https://github.com/stride3d/stride-community-toolkit/pull/193