docs: add work-in-progress banner to README

.vscode/launch.json

@@ -0,0 +1,17 @@
+{
+    // Use IntelliSense to learn about possible attributes.
+    // Hover to view descriptions of existing attributes.
+    // For more information, visit: https://go.microsoft.com/fwlink/?linkid=830387
+    "version": "0.2.0",
+    "configurations": [
+
+        {
+            "name": "Python Debugger: Simple.py",
+            "type": "debugpy",
+            "request": "launch",
+            "program": "${workspaceFolder}/examples/simple.py",
+            "console": "integratedTerminal",
+            "envFile": "${workspaceFolder}/.env"
+        }
+    ]
+}

README.md

@@ -3,6 +3,8 @@
 [![CI](https://github.com/phasenexa/nexa-marketdata/actions/workflows/ci.yml/badge.svg)](https://github.com/phasenexa/nexa-marketdata/actions/workflows/ci.yml)
 [![codecov](https://codecov.io/gh/phasenexa/nexa-marketdata/graph/badge.svg?token=wuud4Aly4u)](https://codecov.io/gh/phasenexa/nexa-marketdata)
 
+> **Work in progress.** This library is under active development. APIs may change without notice.
+
 A unified Python client for European power market data sources: Nord Pool, EPEX SPOT, ENTSO-E Transparency Platform, and EEX.
 
 Handles 15-minute MTU resolution, rate limiting, response caching, timezone normalisation, and format differences across exchanges. Part of the [Phase Nexa](https://phasenexa.com) ecosystem.

examples/simple.py

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+import datetime
+
+from nexa_marketdata import NexaClient
+from nexa_marketdata.types import BiddingZone, Resolution
+
+def main():
+    client = NexaClient()
+    prices = client.day_ahead_prices(
+        zone=BiddingZone.NO2,
+        start=datetime.date(2026, 3, 16),
+        end=datetime.date(2026, 3, 16),
+    )
+
+    print(f"Rows: {len(prices)}")
+    print(f"Index timezone: {prices.index.tz}")
+    print(f"Dtype: {prices['price_eur_mwh'].dtype}")
+    prices.head()
+
+if __name__ == '__main__':
+    main()