Add offset to commented out code, expand explanation

Author: tekktrik

examples/vl6180x_simpletest.py

@@ -17,7 +17,9 @@
 
 # Create sensor instance.
 sensor = adafruit_vl6180x.VL6180X(i2c)
-# sensor = adafruit_vl6180x.VL6180X(i2c) # This would add a +10 millimeter offset to measurements:
+# You can add an offset to distance measurements here (e.g. calibration)
+# Swapping for the following would add a +10 millimeter offset to measurements:
+# sensor = adafruit_vl6180x.VL6180X(i2c, offset=10)
 
 # Main loop prints the range and lux every second:
 while True: