Document SARIF integration guide for scanner authors

[rdwj]

Guide for authors of other SAST tools who want to embed STIG metadata in their SARIF output for optimal Stigcode consumption.

Acceptance Criteria:

• Document the properties.stigIds convention
• Document the properties.nist80053 convention
• Provide example SARIF snippets showing enriched rule metadata
• Explain how Stigcode uses explicit metadata vs. CWE fallback
• Include validation command: stigcode validate-sarif <file> to check metadata completeness