Add simple blink sketch for quick testing.

src/main.cpp

@@ -0,0 +1,15 @@
+#include <Arduino.h>
+
+void setup() {
+  // put your setup code here, to run once:
+  pinMode(2,OUTPUT);
+  
+}
+
+void loop() {
+  digitalWrite(2,HIGH);
+  sleep(1);
+  digitalWrite(2,LOW);
+  sleep(1);
+  
+}