Add some notice for downgrading to CE

doc/downgrade_ee_to_ce/README.md

@@ -46,6 +46,19 @@ $ sudo gitlab-rails runner "Service.where(type: ['JenkinsService', 'JenkinsDepre
 $ bundle exec rails runner "Service.where(type: ['JenkinsService', 'JenkinsDeprecatedService']).delete_all" production
 ```
 
+### Secret variables environment scopes
+
+If you're using this feature, and if you have variables sharing the same
+key however having different scopes in a project, then you might want to
+revisit the setting for those variables.
+
+In CE scopes are completely ignored, therefore you could accidentally get a
+variable which you're not expecting for a particular environment. Make sure
+that you have the right variables in this case.
+
+Data is completely preserved, so you could always upgrade back to EE and
+restore the behavior if you leave it alone.
+
 ## Downgrade to CE
 
 After performing the above mentioned steps, you are now ready to downgrade your