在readme.txt修改后，增加一个新文件，即本文件LIENCE.txt，执行git status，git add readme.txt LIENCE.txt ,git status
$ git status
On branch master
Changes not staged for commit:
  (use "git add <file>..." to update what will be committed)
  (use "git restore <file>..." to discard changes in working directory)
        modified:   readme.txt

Untracked files:
  (use "git add <file>..." to include in what will be committed)
        LIENCE.txt

no changes added to commit (use "git add" and/or "git commit -a")

lcy@lcy-pc MINGW64 /d/only_test_git (master)
$ git add readme.txt LIENCE.txt

lcy@lcy-pc MINGW64 /d/only_test_git (master)
$ git commit -m "测试git暂存区(stage)是怎么工作的"
[master 81b58e7] 测试git暂存区(stage)是怎么工作的
 2 files changed, 3 insertions(+)
 create mode 100644 LIENCE.txt

lcy@lcy-pc MINGW64 /d/only_test_git (master)
$ git status
On branch master
nothing to commit, working tree clean