Improve how to specify the list of GitHub repositories to use in the Committers macro

    /**
     * The format of the repositories is: {@code (organization name)/(repository name)} where {@code organization name}
     * can be {@code *} to signify all repositories for this organization. For example:
     * <ul>
     *   <li>xwiki/*</li>
     *   <li>xwiki-contrib/application-github-statistics</li>
     * </ul>
     */