由于github仓库中提前建立readme文件，导致git push报错error: failed to push some refs to 'git@github.com:

$ git push -u origin master
To git@github.com:xxx/xxx.git
 ! [rejected]        master -> master (fetch first)
error: failed to push some refs to 'git@github.com:xxx/xxx.git'
hint: Updates were rejected because the remote contains work that you do
hint: not have locally. This is usually caused by another repository pushing
hint: to the same ref. You may want to first integrate the remote changes
hint: (e.g., 'git pull ...') before pushing again.
hint: See the 'Note about fast-forwards' in 'git push --help' for details.

原因： 

GitHub远程仓库中的README.md文件不在本地仓库中。
解决方案：

$ git pull --rebase origin master
$ git push -u origin master