$git clone https://github.com/username/Hello-World.git
$git add README
git操作步骤：
1，git add .
git commit -m 'aaaa'
2,git fetch origin master
3,git merge origin/master
4,git push origin master
//******************本机上传到服务器*************************
$git add .//提交所有文件
$git commit -m 'first commit'
$git remote add origin https://github.com/username/Hello-World.git
$git push origin master
