Added UI package documentation

Author: jamesmcroft

docs/articles/features/ui.md

@@ -5,3 +5,28 @@ title: Using the UI package | MADE.NET
 
 # Using the UI package
 
+The UI package is a base package for building out UI components for native applications for Windows, Android, iOS, macOS, Linux, and the web. 
+
+Its main purpose is to be used by the additional MADE.NET UI packages. However, it can be used to build your own custom UI elements for your own applications.
+
+## Building custom controls for Windows or Uno Platform applications
+
+The `MADE.UI.Controls.Control` is an extension to the [`Windows.UI.Xaml.Controls.Control`](https://docs.microsoft.com/en-us/uwp/api/windows.ui.xaml.controls.control) that provides additional base components to make it easier to build custom controls.
+
+For detail on building the custom control itself, we highly recommend these resources for information on building them.
+
+- [Nick's .NET Travels - How to create a XAML templated control](https://nicksnettravels.builttoroam.com/tutorial-how-to-create-a-xaml-templated-control/)
+
+With this base class, you get the following additional features to work with.
+
+### IsVisible property
+
+`IsVisible` is a boolean property that controls the `Visibility` state of the control.
+
+When updated, the `IsVisibleChanged` event is fired which can be used to handle additional functions when a control is shown or hidden.
+
+### GetChildView{TView} method
+
+`GetChildView{TView}(string)` is a method which sits on top of the `GetTemplateChild` method of the underlying `Control` class.
+
+The method simplifies the understanding and usability of retrieving child UI elements by retrieving your UI elements in the expected type.