example of a package dependency asset (#9295)

packages/flutter_tools/templates/create/pubspec.yaml.tmpl

@@ -31,6 +31,17 @@ flutter:
   #  - images/a_dot_burr.jpeg
   #  - images/a_dot_ham.jpeg
 
+  # To add assets from package dependencies, first ensure the asset
+  # is in the lib/ directory of the dependency. Then,
+  # refer to the asset with a path prefixed with
+  # `packages/PACKAGE_NAME/`. Note: the `lib/` is implied, do not
+  # include `lib/` in the asset path.
+  #
+  # Here is an example:
+  #
+  # assets:
+  #  - packages/PACKAGE_NAME/path/to/asset
+
   # To add custom fonts to your application, add a fonts section here,
   # in this "flutter" section. Each entry in this list should have a
   # "family" key with the font family name, and a "fonts" key with a