Update Viewer docs for Android and iOS.

Change-Id: I4208221f982ce79b6c8af9aaa05644b0f1f94a5e
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/268680
Reviewed-by: Tyler Denniston <tdenniston@google.com>
Commit-Queue: Jim Van Verth <jvanverth@google.com>
1 file changed