Update InitialContent.md

Author: michael-hawker

Microsoft.Toolkit.Uwp.SampleApp/SamplePages/MarkdownTextBlock/InitialContent.md

@@ -376,11 +376,11 @@ To add an image, it is almost like a link. You just need to add a \! before.
 
 So inline image syntax looks like this:
 
->\!\[Helpers Image](https\://raw.githubusercontent.com/windows-toolkit/WindowsCommunityToolkit/master/Microsoft.Toolkit.Uwp.SampleApp/Assets/Helpers.png)
+>\!\[Helpers Image](https\://raw.githubusercontent.com/windows-toolkit/WindowsCommunityToolkit/main/Microsoft.Toolkit.Uwp.SampleApp/Assets/Helpers.png)
 
 which renders in:
 
-![Helpers Image](https://raw.githubusercontent.com/windows-toolkit/WindowsCommunityToolkit/master/Microsoft.Toolkit.Uwp.SampleApp/Assets/Helpers.png)
+![Helpers Image](https://raw.githubusercontent.com/windows-toolkit/WindowsCommunityToolkit/main/Microsoft.Toolkit.Uwp.SampleApp/Assets/Helpers.png)
 
 Rendering Images is now supported through prefix. use property **UriPrefix**
 
@@ -412,11 +412,11 @@ which renders in:
 
 MarkdownTextblock supports links wrapped with Images. 
 
->\[!\[image](https\://raw.githubusercontent.com/windows-toolkit/WindowsCommunityToolkit/master/build/nuget.png)](https\://docs.microsoft.com/windows/uwpcommunitytoolkit/)
+>\[!\[image](https\://raw.githubusercontent.com/windows-toolkit/WindowsCommunityToolkit/main/build/nuget.png)](https\://docs.microsoft.com/windows/uwpcommunitytoolkit/)
 
 will render into 
 
-[![image](https://raw.githubusercontent.com/windows-toolkit/WindowsCommunityToolkit/master/build/nuget.png)](https://docs.microsoft.com/windows/uwpcommunitytoolkit/)
+[![image](https://raw.githubusercontent.com/windows-toolkit/WindowsCommunityToolkit/main/build/nuget.png)](https://docs.microsoft.com/windows/uwpcommunitytoolkit/)
 
 and when clicked will go to the Linked Page.
 
@@ -425,7 +425,7 @@ MarkdownTextBlock also supports Reference based links.
 ```
 [![image][1]][2]
 
-[1]:https://raw.githubusercontent.com/windows-toolkit/WindowsCommunityToolkit/master/build/nuget.png
+[1]:https://raw.githubusercontent.com/windows-toolkit/WindowsCommunityToolkit/main/build/nuget.png
 [2]:https://docs.microsoft.com/windows/uwpcommunitytoolkit/
 
 ```
@@ -434,7 +434,7 @@ will render into
 
 [![image][1]][2]
 
-[1]:https://raw.githubusercontent.com/windows-toolkit/WindowsCommunityToolkit/master/build/nuget.png
+[1]:https://raw.githubusercontent.com/windows-toolkit/WindowsCommunityToolkit/main/build/nuget.png
 [2]:https://docs.microsoft.com/windows/uwpcommunitytoolkit/
 
 *****