We have recently introduced support of GitHub documentation on the Jenkins Plugin Site. See https://groups.google.com/forum/#!topic/jenkinsci-dev/VSdfVMDIW-A for the announcement. 

Jenkins users seeking documentation will have a better user experience on plugins.jenkins.io than they do on wiki.jenkins.io. At the same time, maintainers can follow the documentation-as-code approach and make documentation changes a part of pull requests. Documentation changes will be reviewed as part of pull requests and documentation contributors will be recognized, especially when combined with Release Drafter. We recommend all plugins to migrate documentation to GitHub.

Steps:

• Select a plugin you want to improve, clone this issue and assign the correct component ID
• Review the plugin page on the Wiki and in the GitHub README. If there is missing information in the README, submit a pull request with the documentation update
• Modify the documentation URL in the project file: https://wiki.jenkins.io/display/JENKINS/Hosting+Plugins#HostingPlugins-Referencingthedocumentationpagefromtheprojectfile

Once the steps are completed and your pull request is merged by the maintainer, the GitHub landing page will be updated. The next time the plugin releases, the documentation will appear on https://plugins.jenkins.io/.