If you have generated your site, but for some reasons, fail to publish it, and/or you hope to use git manually to push it to Github, you can follow following steps:

Step 1: cd <output-dir>（you can get <output-dir> in "Generated Successfully" modal）

Step 2: git init --separate-git-dir ../git_repository

Since now, you can use git as usual to do anything you want, including pushing to remote.