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

* commit '296d84fbd9f04653edef37aede5e3c0663f8945c':
  cherrypick from mnc-io-docs docs: Updated Billing API documentation (for Project Nickel).

Change-Id: If3e7a0663a97f94d46059ed6fdd5b0cc75a0af3c