docs(maintainers): add maintained files for MediaTek SoCs

Change-Id: I2d71b2fef2f2aee507a6e7c4b9b9d8175446a0ca
diff --git a/docs/about/maintainers.rst b/docs/about/maintainers.rst
index 16c41bd..ad125cf 100644
--- a/docs/about/maintainers.rst
+++ b/docs/about/maintainers.rst
@@ -480,6 +480,7 @@
 ^^^^^^^^^^^^^^^^^^^^^^^
 :|M|: Rex-BC Chen <rex-bc.chen@mediatek.com>
 :|G|: `mtk-rex-bc-chen`_
+:|F|: docs/plat/mt\*.rst
 :|F|: plat/mediatek/
 
 Marvell platform ports and SoC drivers