Update gclient solution advisory for WebRTC tests.

We need to run download_from_google_storage --config nowaways before
adding webrtc.DEPS to .gclient, so update the help text to that effect.

R=ajose@chromium.org
BUG=532554,525849

Review URL: https://codereview.chromium.org/1473223002

Cr-Commit-Position: refs/heads/master@{#361618}
3 files changed