Merge branch 'disable-ff-documentation' into 'master'

Adds the command for disabling a feature flag

See merge request gitlab-org/gitlab!20776

doc/development/feature_flags/development.md

@@ -129,3 +129,9 @@ In the rails console (`rails c`), enter the following command to enable your fea
 ```ruby
 Feature.enable(:feature_flag_name)
 ```
+
+Similarly, the following command will disable a feature flag:
+
+```ruby
+Feature.disable(:feature_flag_name)
+```