MAINTAINERS: add Timothy to documentation

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

MAINTAINERS

@@ -43,7 +43,7 @@ QuickTime faststart:
 Miscellaneous Areas
 ===================
 
-documentation                           Stefano Sabatini, Mike Melanson
+documentation                           Stefano Sabatini, Mike Melanson, Timothy Gu
 build system (configure,Makefiles)      Diego Biurrun, Mans Rullgard
 project server                          Árpád Gereöffy, Michael Niedermayer, Reimar Döffinger, Alexander Strasser
 presets                                 Robert Swain