add warning to conditioning

add warning to:
- Readme
- Example Usage
- Function description

Closes #5

README.md

@@ -49,6 +49,14 @@ Note: Installation via the Arduino Library Manager is coming soon.
    Plotter` via the `Tools` menu to observe the measurement values. Note that
    the `Baud Rate` in the corresponding window has to be set to `115200 baud`.
 
+# Conditioning
+
+After each restart of the sensor or when the hotplates have been switched off, the conditioning command must
+be called from idle mode. The conditioning heats the hotplate of the NOx pixel to a different temperature compared
+to the measurement mode enabling a faster switch-on thereafter.
+
+It is recommended to execute the conditioning for 10s, but **10s must not be exceeded** to avoid damage to the sensing material.
+
 # Contributing
 
 **Contributions are welcome!**

examples/exampleUsage/exampleUsage.ino

@@ -40,7 +40,8 @@
 
 SensirionI2CSgp41 sgp41;
 
-// time in seconds needed for NOx conditioning
+// Time in seconds needed for NOx conditioning
+// WARNING: To avoid damage to the sensing material the conditioning must not exceed 10s!
 uint16_t conditioning_s = 10;
 
 void setup() {

src/SensirionI2CSgp41.h

@@ -61,6 +61,8 @@ class SensirionI2CSgp41 {
      * the sgp41_measure_raw command while the NOx pixel will be operated at a
      * different temperature for conditioning. This command returns only the
      * measured raw signal of the VOC pixel SRAW_VOC as 2 bytes (+ 1 CRC byte).
+     * 
+     * WARNING: To avoid damage to the sensing material the conditioning must not exceed 10s!
      *
      * @param defaultRh Default conditions for relative humidty.
      *