Update serial.mdx

add arduino .ino code
tested with arduini mini pro with pir sensor connected to pin 2

docs/configuration/module-config/serial.mdx

@@ -245,3 +245,30 @@ while True:
         time.sleep(30)
     time.sleep(0.5)
 ```
+
+#### Circuit .ino Code
+
+```
+int LED = 13;             // the pin that the LED is atteched to
+int PIR = 2;              // the pin that the sensor is atteched to
+
+void setup() {
+  pinMode(LED, OUTPUT);   // initalize LED as an output
+  pinMode(PIR, INPUT);    // initialize sensor as an input
+  Serial.begin(9600);     // initialize serial
+}
+
+void loop(){
+  if (digitalRead(PIR) == HIGH) { // check if the sensor is HIGH
+    digitalWrite(LED, HIGH);      // turn LED ON 
+    Serial.write(":Motion!:"); 
+    delay(10000);                   // delay 100 milliseconds 
+  } 
+  else {
+    digitalWrite(LED, LOW);       // turn LED OFF
+    Serial.write("Motion stopped!");
+    delay(10000);                   // delay 100 milliseconds
+  }
+}
+```
+```