使用git上传代码时 出现错误：
error: The following untracked working tree files would be overwritten by merge:
gifts/.DS_Store
Please move or remove them before you can merge.
Aborting
使用 git clean -d -fx 即可解决
执行后：
Removing .DS_Store
Removing gifts/.DS_Store
Removing gifts/gifts/.DS_Store
Removing gifts/gifts/Navigation/.DS_Store
Removing gifts/gifts/Navigation/DateSource/.DS_Store
Removing gifts/gifts/Navigation/Pictures/.DS_Store
将目录下的.DS_Store文件全部删除；
不过使用git clean -d -fx时需要注意 会删除掉没有add到仓库的文档 大家要谨慎操作！！！
执行 git add .时出现错误:
If no other git process is currently running, this probably means a
git process crashed in this repository earlier. Make sure no other git
process is running and remove the file manually to continue.
解决方案:
rm -f ./.git/index.lock
git 版本回退:
git reflog
git reset --hard
