github changes not staged for commit

在文件夹中删除文件后git commit，出现

On branch master
Changes not staged for commit:

和

no changes added to commit

解决：
http://stackoverflow.com/questions/10721624/github-changes-not-staged-for-commit
git add .

原理：

It is also common to recursively add all files in a new project by specifying the
current working directory like this:

git add .

.
Since Git will recursively add all files under a directory you give it, if you give it the current working directory, it will simply start tracking every file there. In this case, a

git
add .

would have done the same thing as a

git
add README hello.rb

, or for that matter so would

git
add *

, but that's only because we don't have subdirectories which the

*

would
not recurse into.
http://gitref.org/basic/