使用github时，遇到问题：
Permission denied (publickey).
fatal: Could not read from remote repository.
解决办法：
1 打开命令行，执行如下命令：
ssh-keygen -t rsa -b 4096 -C "your_email@example.com"
此命令会生成两个文件，id_rsa,和id_rsa.pub.
当提示"Enter a file in which to save the key," 时，按回车，将生成的文件存储到默认位置，然后再根据提示按两次回车
2 执行如下命令，打开ssh-agent
eval "$(ssh-agent -s)"
Add your SSH private key to the ssh-agent. If you created your key with a different name, or if you are adding an existing key that has a different name, replace id_rsa in the command with the name of your private key file.
3 执行如下命令，将ssh key 添加到ssh-agent:
ssh-add ~/.ssh/id_rsa
4 将我们生成的key添加到github 账户中，添加办法：点这里.
