docs: media: add usage documentation for the VDA/VEA unittests

This document used to be maintained as a Google Docs, but having it
available in the Chromium repository makes it much easier to access for
partners.

BUG=None
TEST=Generated and checked HTML using Markdown.

Change-Id: I790504be2720150cebee151a585a2435ac35a494
Reviewed-on: https://chromium-review.googlesource.com/c/1322174
Commit-Queue: Alexandre Courbot <[email protected]>
Reviewed-by: Hirokazu Honda <[email protected]>
Cr-Commit-Position: refs/heads/master@{#606390}
diff --git a/docs/README.md b/docs/README.md
index f0cf6bf..04b09b743 100644
--- a/docs/README.md
+++ b/docs/README.md
@@ -282,6 +282,8 @@
 *   [Autoplay of HTMLMediaElements](media/autoplay.md) - How HTMLMediaElements
     are autoplayed.
 *   [Piranha Plant](piranha_plant.md) - Future architecture of MediaStreams
+*   [Video Decode/Encode Accelerator Tests](media/gpu/vdatest_usage.md) - How to
+    use the accelerated video decoder/encoder test programs.
 
 ### Accessibility
 *   [Accessibility Overview](accessibility/overview.md) - Overview of