Clearly document use cases and limitations for this code

Given that there are complementary solutions to SCSP, we should clearly define when SCSP is a good solution, especially compared to ASH and Probe.

Specifically, think about where in the Pythia flow SCSP would differentiate itself: https://review.pythia.architecture.aws.dev/home/scenarios/sa

Certain positive differentiators:
- Requirements for code to stay within customer-owned infrastructure
- Customer wants transparency on what code is being executed
- Consultant wants to avoid usage of containers

Certain limitations:
- Downloads tools from the Internet
- Supports only CodeCommit at the moment

Start with the Pythia scenarios page linked in the issue and review how SCSP compares with ASH and Probe. Document where SCSP is a good fit, including its listed differentiators, and clearly state its limitations around Internet downloads and CodeCommit-only support. Done means these use cases and limitations are clearly captured for users evaluating SCSP.

Written by the indexing model from the issue text.