Add smcgruer@ as an editor

Author: stephenmcgruer

Overview.bs

@@ -11,6 +11,7 @@ Abstract: Defines an API and markup for creating animations that are either
 Editor: Brian Birtles <bbirtles@mozilla.com>
 Editor: Botond Ballo <botond@mozilla.com>
 Editor: Mantaroh Yoshinaga <mantaroh@mozilla.com>
+Editor: Stephen McGruer <smcgruer@google.com>
 !Issue Tracking: <a href="https://github.com/WICG/scroll-animations/issues">GitHub Issues</a>
 </pre>
 <pre class=anchors>