ref: https://cwiki.apache.org/confluence/pages/viewpage.action?pageId=65865114
The following example is merging Pull-Request-9 to develop branch.
# Project Setup from Gitbox
git clone https://gitbox.apache.org/repos/asf/incubator-marvin.git
cd incubator-marvin
git remote add mirror https://github.com/apache/incubator-marvin.git
# Update Branch
git checkout develop
git pull origin develop
# Merge Pull Request to Gitbox
git fetch mirror pull/9/head:pr-9
git merge pr-9
git push origin develop
git branch -d pr-9