Add NeoPixel

src/main.cpp

 #include <Arduino.h>
+#include <Adafruit_NeoPixel.h>
+
+#define NEOPIXEL_PIN 6
+#define NEOPIXEL_LEN 105
+
+Adafruit_NeoPixel pixels(NEOPIXEL_LEN, NEOPIXEL_PIN, NEO_GRB + NEO_KHZ800);
 
 void setup() {
   pinMode(LED_BUILTIN, OUTPUT);
+  pixels.begin();
 }
 
+int pos = 0;
+
 void loop() {
+  for (int i = 0; i < NEOPIXEL_LEN; i++) {
+    pixels.setPixelColor(i, 0xFFFFFF);
+  }
+  pixels.setPixelColor(pos, 0xFF0000);
+  pixels.show();
+  pos = (pos + 1) % NEOPIXEL_LEN;
+
   digitalWrite(LED_BUILTIN, HIGH);
   delay(500);
   digitalWrite(LED_BUILTIN, LOW);