Merge "cherrypick from mnc-io-docs docs: Updated Billing API documentation (for Project Nickel)." into mnc-io-docs am: 296d84fbd9 am: 59ce20df8c
am: 482bf05a8f

* commit '482bf05a8f192b1978362108c23bc24f6dfe529e':
  cherrypick from mnc-io-docs docs: Updated Billing API documentation (for Project Nickel).

Change-Id: I98bfa66b0cdfe7c2447c2a675cfd81c3ac750f3e