感谢古月up：https://www.bilibili.com/video/BV1zt411G7Vn?p=13
1、在catkin_ws/src下创建功能包：
catkin_create_pkg learning_service roscpp rospy std_msgs geometry_msgs turtlesim
2、
add_executable(turtle_spawn src/turtle_spawn.cpp)
target_link_libraries(turtle_spawn ${catkin_LIBRARIES})
3、编译并运行客户端