Add VERSION.md for firmware 6.0.0 details

Added version information for firmware 6.0.0 including highlights and details.

VERSION.md

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+# Electricity Price Ticker – Version Information
+
+## Current firmware
+
+- **Version:** 6.0.0  
+- **Release date:** 2026-01-27  
+- **Target MCU:** Seeed XIAO ESP32‑C3  
+- **Display:** 20x4 I²C LCD (PCF8574, default address `0x27`)  
+- **API endpoint:** `https://api.energy-charts.info/price?bzn=SI`  
+- **Resolution:** 15‑minute intervals, hourly averages for overview  
+
+## Highlights of v6.0.0
+
+- Single **daily fetch** (on boot / after midnight) instead of hourly.
+- **NVS storage** of daily data for resilience to power outages.
+- Robust midnight rollover and retry logic:
+  - First immediate fetch.
+  - Up to 5 × 10‑minute retries.
+  - Then top‑of‑hour retries until successful.
+- Prevents yesterday’s prices from ever being shown as today’s.
+- Secondary info menu extended with **NVS status** and clear version label.
+
+For full details, see:
+
+- [CHANGELOG.md](./CHANGELOG.md)
+- [README.md](./README.md)