Adjust CONTRIBUTING.md to mention tests

Also make scrollable_positioned_list_example non-publishable.

Author: jamesderlin

AUTHORS

@@ -1,5 +1,5 @@
 # Below is a list of people and organizations that have contributed
-# to the Flutter project. Names should be added to the list like so:
+# to the Flutter Widgets project. Names should be added to the list like so:
 #
 #   Name/Organization <email address>
 

CONTRIBUTING.md

@@ -40,7 +40,7 @@ keep the code consistent and avoid common pitfalls.
 
 You must complete the
 [Contributor License Agreement](https://cla.developers.google.com/clas). You can
-do this online, and it only takes a minute. If you've never submitted code
+do this online, and it takes only a minute. If you've never submitted code
 before, you must add your (or your organization's) name and contact info to the
 [AUTHORS](AUTHORS) file.
 
@@ -58,13 +58,12 @@ To send us a pull request:
   go to `https://github.com/google/flutter.widgets` and click the
   "Compare & pull request" button
 
-Please make sure all your checkins have detailed commit messages explaining the patch.
+Please make sure all your checkins have detailed commit messages explaining 
+what the patch does and *why*. **Changes to code behavior should include unit
+tests** that would fail without the change.
 
 Once you've gotten an LGTM from a project maintainer and once your PR has
 received the green light from all our automated testing (Travis, Appveyor, etc),
-one of the project maintainers will merge the changes to our internal repo. This
+one of the project maintainers will test the changes to our internal repo. This
 might cause test failures that need to be debugged internally so we might make
 further suggestions on your PR.
-
-Once the internal change is submitted to the private repo, we will run our sync
-scripts to bring this repo up to date. At that point, your PR will be closed.

packages/scrollable_positioned_list/example/pubspec.yaml

@@ -1,5 +1,7 @@
 name: scrollable_positioned_list_example
 
+publish_to: 'none'
+
 environment:
   sdk: '>=2.12.0-0 <3.0.0'
   flutter: '>=1.13.8'