android_studio.md: Mention Gradle wrapper, make --canary more prominent

NOTRY=true  # Doc change

Change-Id: Ib1f0379d78b2c668fa8b9541f0427fb13eab177e
Reviewed-on: https://chromium-review.googlesource.com/700478
Reviewed-by: Peter Wen <wnwen@chromium.org>
Commit-Queue: Peter Wen <wnwen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#506386}
1 file changed