cipd: Fix build.py docs formatting, add "Verifying a package" section.
cipd: Fix build.py docs formatting, add "Verifying a package" section.

R=nodir@chromium.org
BUG=

Review URL: https://codereview.chromium.org/1003603002

nicko96/Chrome-Infra,nicko96/Chrome-Infra,nicko96/Chrome-Infra,nicko96/Chrome-Infra,nicko96/Chrome-Infra