Merge branch 'man-rake-check' into 'master'

Man rake check

Related to: https://dev.gitlab.org/gitlab/organization/issues/12

In a previous release, it happened that the check was not yet updated, eventhough an updated GitLab Shell version was recommended.

doc/release/manual_testing.md

@@ -46,3 +46,7 @@ Use the [support document](https://docs.google.com/document/d/1cAHvbdFE6zR5WY-zh
 ## Upgrader
 - Upgrade from the previous release
 - Run the upgrader script in this release (it should not break)
+
+## Rake tasks
+- Check if rake gitlab:check is updated and works
+- Check if rake gitlab:env:info is updated and works