Add DevOps Adoption feature flag to docs

This adds an explanation of the DevOps Adoption feature flag to the
documentation under a new section.

doc/user/admin_area/analytics/dev_ops_report.md

@@ -59,3 +59,21 @@ DevOps Adoption allows you to:
 - Find the groups that have adopted certain features and can provide guidance to other groups on how to use those features.
 
 ![DevOps Report](img/dev_ops_adoption_v13_7.png)
+
+### Disable or enable DevOps Adoption
+
+DevOps Adoption is deployed behind a feature flag that is **enabled by default**.
+[GitLab administrators with access to the GitLab Rails console](../../../administration/feature_flags.md)
+can opt to disable it.
+
+To disable it:
+
+```ruby
+Feature.disable(:devops_adoption_feature)
+```
+
+To enable it:
+
+```ruby
+Feature.enable(:devops_adoption_feature)
+```