Move pico_tone example to new Tone section with name christmas melody

Author: jcarranz97

README.md

@@ -244,7 +244,6 @@ App|Description
 [hello_pwm](pwm/hello_pwm) | Minimal example of driving PWM output on GPIOs.
 [led_fade](pwm/led_fade) | Fade an LED between low and high brightness. An interrupt handler updates the PWM slice's output level each time the counter wraps.
 [measure_duty_cycle](pwm/measure_duty_cycle) | Drives a PWM output at a range of duty cycles, and uses another PWM slice in input mode to measure the duty cycle.
-[pico_tone](pwm/pico_tone) | Play a christmas melody :notes::christmas_tree: by generating square waves with PWM and a Buzzer :speaker:.
 
 ### Reset
 
@@ -369,3 +368,9 @@ At the time of writing, there is only one dual example available:
 App|Description
 ---|---
 [hello_watchdog](watchdog/hello_watchdog) | Set the watchdog timer, and let it expire. Detect the reboot, and halt.
+
+### Tone
+
+App|Description
+---|---
+[christmas_melody](tone/christmas_melody) | Play a christmas melody :notes::christmas_tree: with a Buzzer :speaker:.