Link from android-binary-size docs -> gerrit plugin

Change-Id: I532b9e054a047bffa34fddaee6e69c2b0795b204
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2391215


Auto-Submit: Andrew Grieve <agrieve@chromium.org>
Reviewed-by: Mohamed Heikal <mheikal@chromium.org>
Commit-Queue: Mohamed Heikal <mheikal@chromium.org>
Cr-Commit-Position: refs/heads/master@{#804416}