Add Confidential Epic docs

For confidential epics, add relevant documentation

doc/user/group/epics/index.md

@@ -31,6 +31,7 @@ To learn what you can do with an epic, see [Manage epics](manage_epics.md). Poss
 - [Reopen a closed epic](manage_epics.md#reopen-a-closed-epic)
 - [Go to an epic from an issue](manage_epics.md#go-to-an-epic-from-an-issue)
 - [Search for an epic from epics list page](manage_epics.md#search-for-an-epic-from-epics-list-page)
+- [Make an epic confidential](manage_epics.md#make-an-epic-confidential)
 - [Manage issues assigned to an epic](manage_epics.md#manage-issues-assigned-to-an-epic)
 - [Manage multi-level child epics **(ULTIMATE)**](manage_epics.md#manage-multi-level-child-epics-ultimate)
 

doc/user/group/epics/manage_epics.md

@@ -18,10 +18,7 @@ selected group. From your group page:
 1. Go to **Epics**.
 1. Click **New epic**.
 1. Enter a descriptive title.
-1. To make the new epic confidential, select the **Make this epic confidential** checkbox
-   ([introduced](https://gitlab.com/gitlab-org/gitlab/-/issues/213068) in
-   [GitLab Ultimate](https://about.gitlab.com/pricing/) 13.0). **(ULTIMATE)**
-1. Click **Create epic** button.
+1. Click **Create epic**.
 
 You will be taken to the new epic where can edit the following details:
 
@@ -34,7 +31,7 @@ You will be taken to the new epic where can edit the following details:
 An epic's page contains the following tabs:
 
 - **Epics and Issues**: epics and issues added to this epic. Child epics, and their issues, are shown in a tree view.
-  - Click on the <kbd>></kbd> beside a parent epic to reveal the child epics and issues.
+  - Click the <kbd>></kbd> beside a parent epic to reveal the child epics and issues.
   - Hover over the total counts to see a breakdown of open and closed items.
 - **Roadmap**: a roadmap view of child epics which have start and due dates.
 
@@ -124,6 +121,36 @@ The sort option and order is saved and used wherever you browse epics, including
 
 ![epics sort](img/epics_sort.png)
 
+## Make an epic confidential
+
+> - [Introduced](https://gitlab.com/gitlab-org/gitlab/-/issues/213068) in [GitLab Ultimate](https://about.gitlab.com/pricing/) 13.0.
+> - It's deployed behind a feature flag, disabled by default.
+> - It's disabled on GitLab.com.
+> - It's not recommended for production use.
+> - To use it in GitLab self-managed instances, ask a GitLab administrator to [enable it](#enable-confidential-epics-premium-only). **(PREMIUM ONLY)**
+
+When you're creating an epic, you can make it confidential by selecting the **Make this epic
+confidential** checkbox.
+
+### Enable Confidential Epics **(PREMIUM ONLY)**
+
+The Confidential Epics feature is under development and not ready for production use. It's deployed behind a
+feature flag that is **disabled by default**.
+[GitLab administrators with access to the GitLab Rails console](../../../administration/feature_flags.md)
+can enable it for your instance.
+
+To enable it:
+
+```ruby
+Feature.enable(:confidential_epics)
+```
+
+To disable it:
+
+```ruby
+Feature.disable(:confidential_epics)
+```
+
 ## Manage issues assigned to an epic
 
 ### Add an issue to an epic