print startup tips (#372)

### What problem were solved in this pull request?

Problem:
While people are learning about miniob, they don't know the owner of the
project.

### What is changed and how it works?
Printing copyright information when starting observer and obclient.

src/obclient/client.cpp

@@ -145,8 +145,20 @@ int init_tcp_sock(const char *server_host, int server_port)
   return sockfd;
 }
 
+const char *startup_tips = R"(
+Welcome to the OceanBase database implementation course.
+
+Copyright (c) 2021 OceanBase and/or its affiliates.
+
+Learn more about OceanBase at https://github.com/oceanbase/oceanbase
+Learn more about MiniOB at https://github.com/oceanbase/miniob
+
+)";
+
 int main(int argc, char *argv[])
 {
+  printf("%s", startup_tips);
+
   const char  *unix_socket_path = nullptr;
   const char  *server_host      = "127.0.0.1";
   int          server_port      = PORT_DEFAULT;

src/observer/main.cpp

@@ -165,10 +165,22 @@ void quit_signal_handle(int signum)
   pthread_create(&tid, nullptr, quit_thread_func, (void *)(intptr_t)signum);
 }
 
+const char *startup_tips = R"(
+Welcome to the OceanBase database implementation course.
+
+Copyright (c) 2021 OceanBase and/or its affiliates.
+
+Learn more about OceanBase at https://github.com/oceanbase/oceanbase
+Learn more about MiniOB at https://github.com/oceanbase/miniob
+
+)";
+
 int main(int argc, char **argv)
 {
   int rc = STATUS_SUCCESS;
 
+  cout << startup_tips;
+
   set_signal_handler(quit_signal_handle);
 
   parse_parameter(argc, argv);