Update readme to reflect my involvement

Author: zturtleman

README.md

@@ -573,7 +573,6 @@ Maintainers
   * Tim Angus <tim@ngus.net>
   * Tony J. White <tjw@tjw.org>
   * Jack "Mr. Nuclear Monster" Slater <jack@ioquake.org>
-  * Zack Middleton <zturtleman@gmail.com>
 
 Significant contributions from
 
@@ -585,5 +584,6 @@ Significant contributions from
   * optical <alex@rigbo.se>
   * Aaron Gyes <floam@aaron.gy>
   * surrealchemist
+  * Zack Middleton <zturtleman@gmail.com>