docs/esp32: Fix machine.Timer quickref to specify HW timers.

Also remove trailing spaces on other lines.

docs/esp32/quickref.rst

@@ -118,17 +118,21 @@ Use the :mod:`time <utime>` module::
 Timers
 ------
 
-Virtual (RTOS-based) timers are supported. Use the :ref:`machine.Timer <machine.Timer>` class
-with timer ID of -1::
+The ESP32 port has four hardware timers. Use the :ref:`machine.Timer <machine.Timer>` class
+with a timer ID from 0 to 3 (inclusive)::
 
     from machine import Timer
 
-    tim = Timer(-1)
-    tim.init(period=5000, mode=Timer.ONE_SHOT, callback=lambda t:print(1))
-    tim.init(period=2000, mode=Timer.PERIODIC, callback=lambda t:print(2))
+    tim0 = Timer(0)
+    tim0.init(period=5000, mode=Timer.ONE_SHOT, callback=lambda t:print(0))
+
+    tim1 = Timer(1)
+    tim1.init(period=2000, mode=Timer.PERIODIC, callback=lambda t:print(1))
 
 The period is in milliseconds.
 
+Virtual timers are not currently supported on this port.
+
 .. _Pins_and_GPIO:
 
 Pins and GPIO