Add content for router outlets (#2236)

* Update 101-router-outlets.md

* Update 101-router-outlets.md

content/roadmaps/104-angular/content/107-routing/101-router-outlets.md

@@ -1 +1,8 @@
-# Router outlets
+# Router outlets
+
+The router-outlet is a directive that's available from the @angular/router package and is used by the router to mark where in a template, a matched component should be inserted.
+
+Thanks to the router outlet, your app will have multiple views/pages and the app template acts like a shell of your application. Any element, you add to the shell will be rendered in each view, only the part marked by the router outlet will be changed between views.
+
+<ResourceGroupTitle>Free Content</ResourceGroupTitle>
+<BadgeLink colorScheme='blue' badgeText='Official Website' href='https://angular.io/api/router/RouterOutle'>Understanding Router Outlets</BadgeLink>