Forking Xamarin.Forms - Howto

I found a bug deep in Xamarin.Forms 3.4 and wanted to diagnose it, so I forked the code but couldn't get it to compile etc.

The instructions on the Xamarin site for forking and creating a Nuget package to use in my project is very out of date.

I couldn't figure it out after an hour so had to give up.

Any new instructions on how to create a Nuget so we can debug/create PRs ?

Ian