Add documentation regarding working groups (#10255)

* initial draft

* add group

* fix wg section

CONTRIBUTING.md

@@ -18,6 +18,7 @@ We hope you'll become an ongoing participant in our open source community but we
   * [Discussion channels](#discussion-channels)
   * [Weekly status updates](#weekly-status-updates)
   * [Weekly design reviews](#weekly-design-reviews)
+  * [Working groups](#working-groups)
   * [See Also](#see-also)
 
 ## Reporting issues with AMP
@@ -126,6 +127,10 @@ We encourage everyone who is actively contributing to AMP to add a comment to th
 
 The community holds weekly engineering [design reviews](./contributing/design-reviews.md) via video conference.  We encourage everyone in the community to participate in these discussions and to bring their designs for new features and significant bug fixes to these reviews.
 
+### Working groups
+
+AMP Project [working groups](./contributing/working-groups.md) bring together parties with related interests to discuss ideas for how AMP can evolve and to receive updates on new features and changes in AMP that are relevant to the group.
+
 ### See Also
 
 * [Code of conduct](CODE_OF_CONDUCT.md)

contributing/working-groups.md

@@ -0,0 +1,9 @@
+# Working groups
+
+AMP Project working groups bring together parties with related interests to discuss ideas for how AMP can evolve and to receive updates on new features and changes in AMP that are relevant to the group.
+
+Working groups include a group email alias as well as periodic video conferences (over Google Hangouts).
+
+The News Publisher Working Group is currently our only active working group.  See the [amp-news-publishers-wg Google group](https://groups.google.com/forum/#!forum/amp-news-publishers-wg) to express interest in joining this working group.
+
+We are actively exploring the creation of other working groups and will update this page as new working groups are created.