Add a comment regarding the LED pin

src/main.rs

@@ -53,6 +53,11 @@ fn main() -> ! {
         &mut pac.RESETS,
     );
 
+    // This is the correct pin on the Raspberry Pico board. On other boards, even if they have an
+    // on-board LED, it might need to be changed.
+    // Notably, on the Pico W, the LED is not connected to any of the RP2040 GPIOs. If you have
+    // a Pico W and want to toggle a LED with a simple GPIO output pin, you can connect an external
+    // LED to one of the GPIO pins, and reference that pin here.
     let mut led_pin = pins.led.into_push_pull_output();
 
     loop {