Fix doc

Author: Morten Nielsen

docs/concepts/NumberBox.md

@@ -1,6 +1,6 @@
 ## `NumberBox<T>`
 
-Port of WinUI's NumberBox control to support generic number types.
+Port of WinUI's [NumberBox](https://learn.microsoft.com/en-us/windows/apps/design/controls/number-box) control to support generic number types.
 
 This control supports validation, increment stepping, and computing inline calculations of basic equations such as multiplication, division, addition, and subtraction.
 
@@ -14,6 +14,8 @@ To be able to assign Decimal values to the NumberBoxDecimal control, it can't be
 
 ## Usage
 
+For the most part, you can rely on [Microsoft's NumberBox documentation](https://learn.microsoft.com/en-us/windows/apps/design/controls/number-box) for how to use this control.
+
 Register the WinUIEx xmlns namespace and add one of the specified controls :
 ```xml
  <ex:NumberBoxInt32 Header="NumberBoxInt32" AllowNull="True"
@@ -33,12 +35,8 @@ Register the WinUIEx xmlns namespace and add one of the specified controls :
                 Description="Decimal"
                 PlaceholderText="Enter number" />>
 ```
-to
-```xml
-<winex:WindowEx xmlns:winex="using:WinUIEx" Width="1024" Height="768"  ...>
-```
 
-## Extending with your own number-type
+### Extending with your own number-type
 
 First create a custom subclass of `NumberBox<T>`, for example for `float`:
 
@@ -47,7 +45,7 @@ public class NumberBoxFloat : NumberBox<float>
 {
      public NumberBoxFloat() => DefaultStyleKey = typeof(NumberBoxFloat);
 } 
-```cs
+```
 
 Next duplicate the control template from the other NumberBox controls and update the target type to match the new type name.
 

src/WinUIExtensions.sln

@@ -35,6 +35,7 @@ Project("{2150E333-8FDC-42A3-9474-1A3956D46DE8}") = "concepts", "concepts", "{0B
 		..\docs\concepts\index.md = ..\docs\concepts\index.md
 		..\docs\concepts\Maui.md = ..\docs\concepts\Maui.md
 		..\docs\concepts\MediaPlayer.md = ..\docs\concepts\MediaPlayer.md
+		..\docs\concepts\NumberBox.md = ..\docs\concepts\NumberBox.md
 		..\docs\concepts\Splashscreen.md = ..\docs\concepts\Splashscreen.md
 		..\docs\concepts\toc.yml = ..\docs\concepts\toc.yml
 		..\docs\concepts\TrayIcon.md = ..\docs\concepts\TrayIcon.md