Some comments on the migration documentation

[johanlindfors]

Nice sample and porting instructions, I believe I've found some minor issues though in the README.md...

1. The "Porting main project" code sections are switched, the first one is WPF and the second is WinForms however the text has it the other way around.

2. After having ported the main ui project, you never reference the earlier created library project, I believe something like the following needs to be added (or just add reference with Visual Studio 2019)