Improve sensorpajen.env.example documentation

- Add comments explaining absolute vs relative paths
- Clarify usage for system vs development installations
- Make it clear that SENSOR_CONFIG_FILE/DISCOVERED_SENSORS_FILE
  should use /etc/sensorpajen paths in system installations
- Remove misleading comment about 'relative to project root'

config/sensorpajen.env.example

@@ -5,15 +5,22 @@ MQTT_USER=hasse
 MQTT_PASSWORD=casablanca
 MQTT_CLIENT_ID=mibridge
 
-# Sensor Configuration (relative to project root)
-SENSOR_CONFIG_FILE=config/sensors.json
-DISCOVERED_SENSORS_FILE=config/discovered_sensors.json
+# Sensor Configuration
+# For system installation (/opt/sensorpajen): Use absolute paths
+# SENSOR_CONFIG_FILE=/etc/sensorpajen/sensors.json
+# DISCOVERED_SENSORS_FILE=/etc/sensorpajen/discovered_sensors.json
+#
+# For development installation: Use relative paths (from project root)
+# SENSOR_CONFIG_FILE=config/sensors.json
+# DISCOVERED_SENSORS_FILE=config/discovered_sensors.json
+#
+# If not set, defaults will be used based on installation type
 
 # Application Settings
 WATCHDOG_TIMEOUT=5
 ENABLE_BATTERY=true
 LOG_LEVEL=INFO
-CONFIG_RELOAD_INTERVAL=900  # 15 minutes in seconds
+CONFIG_RELOAD_INTERVAL=900
 
 # ntfy Notifications (optional)
 NTFY_ENABLED=false