Document Tomorrow generated-text workflow

docs/internal/briefing.md

@@ -38,6 +38,10 @@ Outputs:
 Every registered composition entry has a builder. Unknown or unimplemented
 module IDs fail validation instead of being skipped.
 
+Tomorrow Report supports the Daily-style civil-day modules plus
+`tomorrow_planning` and `hourly_forecast`; those outputs feed the Tomorrow
+GeneratedText prompt package and embedded Markdown template.
+
 Hourly Report supports source and valid-period modules that operate over its
 rolling six-hour period: `metadata`, `current_conditions`, `hourly_forecast`,
 `precip_timing`, `alert_digest`, `spc_convective_outlooks`,