git pull和git fetch

参考：

https://zhuanlan.zhihu.com/p/123370920

https://blog.csdn.net/csh1807266489/article/details/137828008

https://www.cnblogs.com/taohuaya/p/10761799.html

https://it.sohu.com/a/800168660_121124363

https://blog.csdn.net/Frank_colo/article/details/133761742

https://www.cnblogs.com/runnerjack/p/9342362.html