Bug 1800886 - Add the webgpu-reviewers group to the contributing doc. r=webgpu-reviewers,ErichDonGubler,jgilbert

Differential Revision: https://phabricator.services.mozilla.com/D162194

docs/contributing/reviews.rst

@@ -68,6 +68,9 @@ Review groups
    * - #gfx-reviewers
      - Changes to Graphics code
      - `Member list <https://phabricator.services.mozilla.com/project/members/122/>`__
+   * - #webgpu-reviewers
+     - Changes to WebGPU code
+     - `Member list <https://phabricator.services.mozilla.com/project/members/170/>`__
    * - #intermittent-reviewers
      - Test manifest changes
      - `Member list <https://phabricator.services.mozilla.com/project/members/110/>`__