Features can scheduled into your Program Increment from the Increment Roadmap screen.
Can I add other issue types to the Roadmap (other than Epics)?
Yes you can add issue types other than Epics onto the Roadmap. When creating a Program, under the Roadmap Board section, select the third option 'I want to schedule other issue types from a dedicated board onto my Program Roadmap' (the first 2 options are strictly for scheduling Epics onto the Roadmap).
Once you have selected this option, under the Roadmap Board section, you need to select the Board where the issues you want to schedule onto your Roadmap live.
Finally, you must choose the Jira issue link type that connects your Roadmap issues to the issues scheduled in the team Sprints.