Add documentation url in samples.json to address PR comment

Microsoft.Toolkit.Uwp.SampleApp/SamplePages/samples.json

@@ -864,7 +864,8 @@
         "About": "Behavior to automatically select the entire content of a TextBox control when it loads",
         "CodeUrl": "https://github.com/windows-toolkit/WindowsCommunityToolkit/tree/master/Microsoft.Toolkit.Uwp.UI/Behaviors/",
         "XamlCodeFile": "AutoSelectBehaviorXaml.bind",
-        "Icon": "/Assets/Helpers.png"
+        "Icon": "/Assets/Helpers.png",
+        "DocumentationUrl": "https://raw.githubusercontent.com/MicrosoftDocs/WindowsCommunityToolkitDocs/master/docs/behaviors/AutoSelectBehavior.md"
       },
       {
         "Name": "Win2d Path Mini Language Parser",