Update readme

README.md

@@ -113,6 +113,30 @@ so learners know the reasoning is provisional.
 guidance, confidence scale, and the workflows an AI agent should
 follow when asked to add or improve entries.
 
+## References
+
+> **⚠ Important: AI-generated content.** The files under `references/`
+> are compiled by an AI agent from the exam catalog and public sources.
+> AI agents make mistakes — they mis-transcribe figures, miscopy table
+> boundaries, and confidently state things that are subtly wrong. **Do
+> not treat these tables as authoritative.** Verify against the primary
+> sources cited in each file (the official IARU Region 1 band plans, the
+> AFuV/AFuG on
+> [gesetze-im-internet.de](https://www.gesetze-im-internet.de/), or the
+> BNetzA catalog itself) before relying on them.
+
+The `references/` directory holds study aids that span many questions —
+lookup tables cross-referenced to the catalog. They are reading material,
+not part of the build, and are **not** bundled into the `.apkg` decks.
+
+- `references/Frequencies.md` — IARU Region 1 band-plan frequency
+  recommendations (HF through microwave), cross-referenced to the exam
+  questions that test them.
+- `references/Call-Signs.md` — call-sign patterns, suffixes, and country
+  prefixes that appear in the catalog.
+- `references/Q-Codes.md` — Q-codes and operating shorthand used in the
+  questions.
+
 ## More
 
 - `CLAUDE.md` — project orientation, pipeline overview.