boot: zephyr: adding indication LED and detect pin debounce

Setting LED to initial level before beginning.
Making comment about BOOT_SERIAL_DETECT_DELAY more clear in Kconfig.

Signed-off-by: Jared Wolff <hello@jaredwolff.com>
diff --git a/boot/zephyr/Kconfig b/boot/zephyr/Kconfig
index cfbdd5e..91247c4 100644
--- a/boot/zephyr/Kconfig
+++ b/boot/zephyr/Kconfig
@@ -475,7 +475,7 @@
 	  mode.
 
 config BOOT_SERIAL_DETECT_DELAY
-	int "Prevents immediate boot into MCUBoot firmware."
+	int "Serial detect pin detection delay time [ms]"
 	default 0
 	help
 	  Used to prevent the bootloader from loading on button press.