Add Xamarin.Forms Notes for professionals (#7372)

* Add Xamarin.Forms Notes for professionals

* Add file type

books/free-programming-books-langs.md

@@ -486,6 +486,7 @@ That section got so big, we decided to split it into its own file, the [BY SUBJE
 * [Threading in C#](http://www.albahari.com/threading/)
 * [Xamarin Community Toolkit Succinctly](https://www.syncfusion.com/succinctly-free-ebooks/xamarin-community-toolkit-succinctly) - Alessandro Del Sole
 * [Xamarin.Forms for macOS Succinctly](https://www.syncfusion.com/ebooks/xamarin_forms_for_mac_os_succinctly) - Alessandro Del Sole
+* [Xamarin.Forms Notes for professionals](https://books.goalkicker.com/XamarinFormsBook/) - Compiled from StackOverflow documentaion (PDF)
 * [Xamarin.Forms Succinctly](https://www.syncfusion.com/ebooks/xamarin-forms-succinctly) - Alessandro Del Sole