Update navigation.md

Change 404 - page not found to correct URL

Author: zandiarash

docs/WinUI/activation.md

@@ -34,4 +34,4 @@ The `HandleActivationAsync` method gets the first `ActivationHandler` that can h
 
 - [Using and extending the generated app](./readme.md)
 - [Handling navigation within the app](./navigation.md)
-- [All docs](../readme.md)
+- [All docs](../README.md)

docs/WinUI/navigation.md

@@ -51,4 +51,4 @@ This project type adds a ShellPage that sets the NavigationService's frame to a
 
 - [Using and extending the generated app](./readme.md)
 - [Handling app activation](./activation.md)
-- [All docs](../readme.md)
+- [All docs](./readme.md)