错误一
原因：local和remote的文件冲突了
错误二
You are not currently on a branch, so I cannot use any
'branch.<branchname>.merge' in your configuration file.
Please specify which remote branch you want to use on the command
line and try again (e.g. 'git pull <repository> <refspec>').
See git-pull(1) for details. 解决方法：
git checkout -b temp
git checkout master (恢复到master repository的状态）
git pull
错误三
原因：When you created your repository on Github, you created a README.md, which is a new commit. your local repository doesn't know about this commit yet.
Hence: update were rejected because the remote contains work that you don't have locally. So the solution is, you may want to first merge the remote changed before pushing agian.
解决方法：
错误四
解决方法: 此方法慎用，会退回到原来不知道多久前的状态，有时gitHub里这个路径下的东西会乱