samples: blinky: add verbose printf output

Add console output to the sample, with the LED status upon a GPIO toggle.

Signed-off-by: Patryk Koscik <pkoscik@antmicro.com>

samples/basic/blinky/README.rst

@@ -40,8 +40,9 @@ Build and flash Blinky as follows, changing ``reel_board`` for your board:
    :goals: build flash
    :compact:
 
-After flashing, the LED starts to blink. If a runtime error occurs, the sample
-exits without printing to the console.
+After flashing, the LED starts to blink and messages with the current LED state
+are printed on the console. If a runtime error occurs, the sample exits without
+printing to the console.
 
 Build errors
 ************

samples/basic/blinky/src/main.c

@@ -4,6 +4,7 @@
  * SPDX-License-Identifier: Apache-2.0
  */
 
+#include <stdio.h>
 #include <zephyr/kernel.h>
 #include <zephyr/drivers/gpio.h>
 
@@ -22,6 +23,7 @@ static const struct gpio_dt_spec led = GPIO_DT_SPEC_GET(LED0_NODE, gpios);
 int main(void)
 {
 	int ret;
+	bool led_state = true;
 
 	if (!gpio_is_ready_dt(&led)) {
 		return 0;
@@ -37,6 +39,9 @@ int main(void)
 		if (ret < 0) {
 			return 0;
 		}
+
+		led_state = !led_state;
+		printf("LED state: %s\n", led_state ? "ON" : "OFF");
 		k_msleep(SLEEP_TIME_MS);
 	}
 	return 0;