[.NET] Document how use use/consume/ship native libraries

[rolfbjarne]

Read about customer's attempts here: #14622 (this issue also lists outdated documentation on our side): we need to do better here.

Outdated documents:

• https://learn.microsoft.com/en-us/xamarin/ios/platform/native-interop

[KiruyaMomochi]

For reference, here is how Xamarin.Android documents it: Using Native Libraries - Xamarin.Android Docs.