Make batch suggestions an alpha feature

As it was put behind a feature flag, default to false.

doc/user/discussions/index.md

@@ -491,7 +491,10 @@ introduced by [#25381](https://gitlab.com/gitlab-org/gitlab/issues/25381).
 
 ### Batch Suggestions
 
-> [Introduced](https://gitlab.com/gitlab-org/gitlab/issues/25486) in GitLab 13.1.
+> - [Introduced](https://gitlab.com/gitlab-org/gitlab/issues/25486) in GitLab 13.1 as an [alpha feature](https://about.gitlab.com/handbook/product/#alpha).
+> - It's deployed behind a feature flag, disabled by default.
+> - It's disabled on GitLab.com.
+> - To use it in GitLab self-managed instances, ask a GitLab administrator to [enable it](#enable-or-disable-batch-suggestions).
 
 You can apply multiple suggestions at once to reduce the number of commits added
 to your branch to address your reviewers' requests.
@@ -512,6 +515,27 @@ to your branch to address your reviewers' requests.
 
    ![A code change suggestion displayed, with the button to apply the batch of suggestions highlighted.](img/apply_batch_of_suggestions_v13_1.jpg "Apply a batch of suggestions")
 
+#### Enable or disable Batch Suggestions
+
+Batch Suggestions is
+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
+# Instance-wide
+Feature.enable(:batched_suggestions)
+```
+
+To disable it:
+
+```ruby
+# Instance-wide
+Feature.disable(:batched_suggestions)
+```
+
 ## Start a thread by replying to a standard comment
 
 > [Introduced](https://gitlab.com/gitlab-org/gitlab-foss/-/issues/30299) in GitLab 11.9