updated README with links (#621)

navigation_and_routing/README.md

@@ -7,29 +7,29 @@ an article explaining Navigator 2.0.
 
 **Navigator 1.0 samples**
 
-* `nav_1/anonymous_routes.dart` - Shows how to use a Navigator to push and pop
+* [nav_1/anonymous_routes.dart](lib/nav_1/anonymous_routes.dart) - Shows how to use a Navigator to push and pop
   anonymous routes (e.g. MaterialPageRoute)
-* `nav_1/named_routes.dart` - Shows how to use define named routes via the `routes`
+* [nav_1/named_routes.dart](lib/nav_1/named_routes.dart) - Shows how to use define named routes via the `routes`
   parameter on MaterialApp, and navigate using Navigator.pushNamed
-* `nav_1/on_generate_route.dart` - Shows how to handle arbitrary named routes
+* [nav_1/on_generate_route.dart](lib/nav_1/on_generate_route.dart) - Shows how to handle arbitrary named routes
   using the `onGenerateRoute` callback defined in the `MaterialApp` constructor.
 
 **Navigator 2.0 samples**
 
-* `nav_2/pages.dart` - Shows how to define a list of [Page] objects on Navigator
+* [nav_2/pages.dart](lib/nav_2/pages.dart) - Shows how to define a list of [Page] objects on Navigator
   declaratively.
-* `nav_2/router.dart` - Full sample that shows a custom RouteInformationParser
+* [nav_2/router.dart](lib/nav_2/router.dart) - Full sample that shows a custom RouteInformationParser
   and RouterDelegate parsing named routes and declaratively building the stack
   of pages for the Navigator.
 
 
 **Advanced**
 
-* `nav_2_advanced/nested_router.dart` - Shows two [RouterDelegate], one nested
+* [nav_2_advanced/nested_router.dart](lib/nav_2_advanced/nested_router.dart) - Shows two [RouterDelegate], one nested
   within the other. A [BottomNavigationBar] can be used to select the route of
   the outer RouterDelegate, and additional routes can be pushed onto the inner
   RouterDelegate / Navigator.
-* `nav_2_advanced/transition_delegate.dart` - Shows how a custom
+* [nav_2_advanced/transition_delegate.dart](lib/nav_2_advanced/transition_delegate.dart) - Shows how a custom
   TransitionDelegate can be used to customized when transition animations are
   shown.