git 添加tab补全

1. 从github获取 git-completion.bash
2. 将git-completion.bash放在/etc/bash_completion.d/ 目录中 cp ./git-completion.bash /etc/bash_completion.d/git-completion.bash
3. 在~/.bashrc中添加如下代码

   if [ -f /etc/bash_completion.d/git-completion.bash ]; then
       . /etc/bash_completion.d/git-completion.bash
   fi
   

4. 执行source ~/.bashrc使其生效
5. ~/.bashrc的执行依赖于~/.bash_profile如果~/.bash_profile不存在则创建该文件并添加如下代码

   if [ -f ~/.bashrc ]; then
       . ~/.bashrc
   fi