feat(hw_cdc): create main.cpp

Adds the minimum Arduino Sketch that will print "Hello World!" in the HW Serial USB CDC port.

Author: SuGlider

idf_component_examples/hw_cdc_hello_world/main/main.cpp

@@ -0,0 +1,10 @@
+#include <Arduino.h>
+
+void setup() {
+  Serial.begin(); // USB CDC doens't need a baud rate
+}
+
+void loop() {
+  Serial.println("Hello world!");
+  delay(1000);
+}