added microsecond timer calculation for sir

cubesatsim/cubesatsim.ino

@@ -2779,6 +2779,10 @@ bool TimerHandler0(struct repeating_timer *t) {
     if (digitalRead(MAIN_PB_PIN) == PRESSED) 
       Serial.println("PB pressed!");  
 //      process_pushbutton();
+  Serial.print("Microseconds: ");
+  Serial.println(micros() - micro_timer);
+  micro_timer = micros();	
+	
   return true;	
 }