Document Module Compatibility Design Pattern

README lacks explanation of how module outputs are designed to match input types where consumed, making it harder for users to understand GRIT's composable architecture.

Add "Module Compatibility" section explaining that module outputs match expected input structures.

Reference discussion: !134 (comment 2268398810)

Definition of Done

• Add section to GRIT README on output/input type matching 👉 Add module compatibility section to README (!226 - merged) • Davis Bickford • 17.11