Add docs for roadmaps in epics

doc/user/group/epics/index.md

@@ -73,6 +73,16 @@ These are dynamic dates in that if milestones are re-assigned to the issues, if
 milestone dates change, or if issues are added or removed from the epic, then
 the re-calculation will happen immediately to set a new dynamic date.
 
+## Roadmap in epics
+
+> [Introduced](https://gitlab.com/gitlab-org/gitlab-ee/issues/7327) in [GitLab Ultimate](https://about.gitlab.com/pricing) 11.10.
+
+If your epic contains one or more [child epics](#multi-level-child-epics) which
+have a [start or due date](#start-date-and-due-date), then you can see a
+[roadmap](../roadmap/index.md) view of the child epics under the parent epic itself.
+
+![Child epics roadmap](img/child_epics_roadmap.png)
+
 ## Reordering issues and child epics
 
 Drag and drop to reorder issues and child epics. New issues and child epics added to an epic appear at the top of the list.

doc/user/group/roadmap/index.md

 # Roadmap **[ULTIMATE]**
 
-> Introduced in [GitLab Ultimate][ee] 10.5.
+> Introduced in [GitLab Ultimate](https://about.gitlab.com/pricing) 10.5.
 
 An Epic within a group containing **Start date** and/or **Due date**
 can be visualized in a form of a timeline (e.g. a Gantt chart). The Epics Roadmap page
@@ -21,6 +21,8 @@ Epics in the view can be sorted by:
 
 Each option contains a button that can toggle the order between **ascending** and **descending**. The sort option and order will be persisted to be used wherever epics are browsed including the [epics list view](../epics/index.md).
 
+Roadmaps can also be [visualized inside an epic](../epics/index.md#roadmap-in-epics).
+
 ## Timeline duration
 
 Starting with [GitLab Ultimate][ee] 11.0, Roadmap supports three different date ranges; Quarters, Months (Default) and Weeks.
@@ -60,5 +62,3 @@ and due date. If an epic doesn't have a due date, the timeline bar fades
 away towards the future. Similarly, if an epic doesn't have a start date, the
 timeline bar becomes more visible as it approaches the epic's due date on the
 timeline.
-
-[ee]: https://about.gitlab.com/pricing