Add documentation to describe minimal elements for creating new building block

[m-goggins]

Context:

When adding a new building block, there are several places in the code base that need to be updated.

Acceptance Criteria:

• A new document has been added to the tutorials section
• The tutorial for creating a new building block includes information on areas of the code base that need to be changed to accommodate the new building blocking, including:
  • phdi-charts
  • phdi-playground terraform
  • .github/codecov.yml
• The tutorial includes a checklist of required items for the building block, including:
  • a completed description.md
  • a tests folder
  • a Dockerfile
  • a requirements.txt file
  • a dev-requirements.txt file
  • a docker-compose.yml file (if appropriate)

[m-goggins]

@robertandremitchell @robertmitchellv Feel free to change/add anything. @robertandremitchell, if you're able to add links to the spots in the phdi-charts and phdi-playground repos that need to be changed, that would be excellent!