同步远程仓库到本地
git pull=git fetch + merge
$ git pull --rebase origin master
error: cannot pull with rebase: You have unstaged changes.
error: please commit or stash them.
有修改了的文件，但是没有提交。这种情况可以用git status查看哪些文件修改了没有提交，可以提交这些文件。或者，放弃这些文件的修改（git restore）
git status
git restore DoctoralDissertationCollection/settings.py
error: The following untracked working tree files would be overwritten by merge:
user/__init__.py
Please move or remove them before you merge.
Aborting
error: could not detach HEAD
有文件没有加入版本控制中，但是下载的新文件和该文件同名，此时，可以删除本地的该文件。
Your branch is up to date with 'origin/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: .idea/workspace.xml
modified: DoctoralDissertationCollection/settings.py
Untracked files:
(use "git add <file>..." to include in what will be committed)
DoctoralDissertationCollection/__pycache__/__init__.cpython-38.pyc
DoctoralDissertationCollection/__pycache__/settings.cpython-38.pyc