add some notes and basic code

include/utils.h

@@ -0,0 +1,17 @@
+#ifndef __UTILS_H__
+#define __UTILS_H__
+
+#include <arpa/inet.h>
+#include <netdb.h>
+#include <netinet/in.h>
+#include <sys/socket.h>
+#include <sys/types.h>
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+// Print every IPs of a hostname
+void print_ips(const char *hostname, const char *port);
+
+#endif