To github.com:gentleni/gitproject.git
 ! [rejected]        master -> master (non-fast-forward)
error: failed to push some refs to 'git@github.com:zzzz/zzzz.git'
hint: Updates were rejected because the tip of your current branch is behind
hint: its remote counterpart. Integrate the remote changes (e.g.
hint: 'git pull ...') before pushing again.
hint: See the 'Note about fast-forwards' in 'git push --help' for details.

原因

在github新建远程仓库的时候选择了新建readme.md，导致冲突

解决

git pull --rebase origin master