Add a How-To document

[aiuto]

• pull information from (design)[https://docs.google.com/document/d/1uwBuhAoBNrw8tmFs-NxlssI6VRolidGYdYqagLqHWt8/edit#]
• and from licenses/spdx/BUILD
• Use case for just labeling your work
  • depend on the release and add license() rules
• Use case for building license inclusion reporting and testing
  • Some reporting for free
  • Recommend that you vendor package in for meaningful compliance