Add links in the sidebar of the Jenkins main page, view tabs and project pages.
Additional Sidebar Linkssection in the main Jenkins configuration page, with settings for link URLs, texts and icons. These links will be shown in the top-level Jenkins pages (main page, user list, build history, My Projects and other project view tabs). Sidebar links for particular jobs may also be added in the job configuration pages.
JENKINS_HOME/userContentdirectory from global config page. (JENKINS-8320)
HUDSON_HOME/userContentdirectory, and for absolute vs in-this-Hudson URLs.