feat: US-018 - Add llms.txt reference to README

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: ivnbogdan

README.md

@@ -155,4 +155,6 @@ uv run mypy .
 
 ## License
 
-[MIT License](LICENSE)
+[MIT License](LICENSE)
+
+For AI/LLM integration instructions, see [llms.txt](./llms.txt)