Include sample template SSP generation in web docs

[danielnaab]

Extended Description As a user drafting a FedRAMP OSCAL SSP, I would like a template document that I can use as a starting point.

Context: a transform exists to generate a sample SSP. This transform could either be better documented, and/or included in the web interface. See: https://github.com/18F/fedramp-automation/blob/master/src/validations/rules/sample-ssp.xsl

Acceptance Criteria

• [ ] Sample SSP generation is accessible to end-users

Definition of Done

• [ ] Acceptance criteria met
• [ ] Unit test coverage of our code > 90% - needs automation story
• [ ] Accessibility tests pass - needs automation story
• [ ] Automated code quality checks pass
• [ ] Security reviewed and reported - check in with Wes on what we could do here
• [ ] Reviewed against plain language guidelines
• [ ] Design QA passed
• [ ] Code must be self-documenting
• [ ] No local tech debt
• [ ] Documentation updated
• [ ] Architectural Decision Record completed as necessary for significant design choices
• [ ] PR reviewed & approved
• [ ] Source code merged