Add LED to timer example

README.md

@@ -150,7 +150,7 @@ MicroPython on the ESP32 has virtual timers and 4 hardware timers. You can use a
 Timers execute a callback, which takes the timer as an argument
 
 ``` python
-from machine import Timer
+from machine import Timer, Pin
 import utime
 
 # Create a virtual timer with ID -1.
@@ -160,10 +160,13 @@ timer = Timer(-1)
 data = [0] * 32
 index = 0
 
+led = Pin(5, Pin.OUT)
+
 def callback(timer):
     global data, index
     data[index] = utime.ticks_ms
     index = (index + 1) % 32
+    led(!led())
 
 # Run the callback once, after 100 ms
 timer.init(mode = Timer.ONE_SHOT, period = 100, callback = callback)