add auth flows

Author: Tyler Whitney

articles/active-directory/develop/index.yml

@@ -26,6 +26,8 @@ landingContent:
         links:
           - text: Authentication basics
             url: authentication-scenarios.md
+          - text: Authentication flows and app scenarios
+            url: authentication-flows-app-scenarios.md
           - text: Best practices
             url: identity-platform-integration-checklist.md
       - linkListType: learn