Update example to note cycle threshold parameter for Arduino Due.

examples/DHTtester/DHTtester.ino

@@ -11,11 +11,22 @@
 //#define DHTTYPE DHT21   // DHT 21 (AM2301)
 
 // Connect pin 1 (on the left) of the sensor to +5V
+// NOTE: If using a board with 3.3V logic like an Arduino Due connect pin 1
+// to 3.3V instead of 5V!
 // Connect pin 2 of the sensor to whatever your DHTPIN is
 // Connect pin 4 (on the right) of the sensor to GROUND
 // Connect a 10K resistor from pin 2 (data) to pin 1 (power) of the sensor
 
+// Initialize DHT sensor for normal 16mhz Arduino
 DHT dht(DHTPIN, DHTTYPE);
+// NOTE: For working with a faster chip, like an Arduino Due or Teensy, you
+// might need to increase the threshold for cycle counts considered a 1 or 0.
+// You can do this by passing a 3rd parameter for this threshold.  It's a bit
+// of fiddling to find the right value, but in general the faster the CPU the
+// higher the value.  The default for a 16mhz AVR is a value of 6.  For an
+// Arduino Due that runs at 84mhz a value of 30 works.
+// Example to initialize DHT sensor for Arduino Due:
+//DHT dht(DHTPIN, DHTTYPE, 30);
 
 void setup() {
   Serial.begin(9600);