Add link to Flutter brand guidelines (flutter#26257)

Tim Sneath · web-flow · commit c944d88788b4 · 2019-01-09T14:52:29.000-08:00
diff --git a/packages/flutter/lib/src/material/flutter_logo.dart b/packages/flutter/lib/src/material/flutter_logo.dart
@@ -7,6 +7,7 @@ import 'package:flutter/widgets.dart';
 import 'colors.dart';
 
 /// The Flutter logo, in widget form. This widget respects the [IconTheme].
+/// For guidelines on using the Flutter logo, visit https://flutter.io/brand.
 ///
 /// See also:
 ///
