CTS Verifier : Append instructions

I have appended instructions to "BYOD_WiFiDataUsageSettingsVisibleTest"

None GMS build doesn't have any work badged application using
Wi-Fi data during this test, so 'All work apps' is not shown
on Wi-Fi data usage. We have to use Wi-Fi data on a work app
by manually to see 'All work apps' on Wi-Fi data usage.

These instructions will help resolve the issue for everyone
and no waivers will be needed in the future.

Bug: 123268619

Change-Id: Ide7cc4b6be6ffa2a68bcb2afeb2c58d2e1e687a3
Signed-off-by: vincent Hwang <vincent.hwang@pointmobile.co.kr>