git执行add命令是报错：
$ git add -A .fatal: Unable to create 'xxx目录/.git/index.lock': File exists.
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.
最简单的处理就是重启电脑，因为你操作了两个git的工作空间，其中前一个git的线程没有退出，所以再操作第二个，提示了当前内容。