Document how to contribute to package OSCAL documents

Create a document that covers:

• Why we have OSCAL documents in BigBang packages
• The basics of OSCAL Component schema (https://pages.nist.gov/OSCAL/reference/latest/component-definition/json-reference/#/component-definition/import-component-definitions)
• How to validate package OSCAL documents against JSON Schema
• Considerations when updating package OSCAL Documents
  • Ensure partyID is consistent throughout all packages, it should not change.
  • New UUID is generated everytime package OSCAL document is modified
• How to add a control-implementation
• A brief explanation of our intentions to aggregate package OSCAL documents into a unified Big Bang OSCAL document.