Merge "docs: Updated Billing API documentation (for Project Nickel)." into mnc-io-docs
am: 5ea88aad9d

* commit '5ea88aad9dcc1ae7e5bc0db0ac390da2b37eb27e':
  docs: Updated Billing API documentation (for Project Nickel).

Change-Id: Ia22ba5823527e56346d697241c525656a5b9c86d