add README

skills/text_to_sql/README.md

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+# Text-to-SQL with Claude
+
+Learn how to generate complex SQL queries from natural language using prompting techniques, self-improvement, and RAG.
+
+## Contents
+
+- `guide.ipynb`: Main tutorial notebook
+- `data/`: Data files for examples and testing
+- `evaluation/`: Evaluation scripts using Promptfoo
+
+For evaluation instructions, see `evaluation/README.md`.