Created basic attention requests docs

https://gitlab.com/gitlab-org/gitlab/-/issues/353235

doc/user/project/merge_requests/index.md

@@ -70,6 +70,53 @@ change and whether you need access to a development environment:
 - [Push changes from the command line](../../../gitlab-basics/start-using-git.md), if you are
   familiar with Git and the command line.
 
+## Request attention to a merge request
+
+> [Introduced](https://gitlab.com/gitlab-org/gitlab/-/issues/343528) in GitLab 14.10 [with a flag](../../../administration/feature_flags.md) named `mr_attention_requests`. Disabled by default.
+
+FLAG:
+On self-managed GitLab, by default this feature is not available. To make it available, ask an administrator to [enable the feature flag](../../../administration/feature_flags.md) named `mr_attention_requests`.
+On GitLab.com, this feature is dependent on the enablement status of the feature flag. Refer to the [enablement issue](https://gitlab.com/gitlab-org/gitlab/-/issues/343528) for details.
+
+To tell a merge request's assignee or reviewer that their attention is
+needed on a merge request, you can request their attention. If an assignee or a
+reviewer has their attention requested on a merge request, the **Attention request**
+icon (**{attention}**) is displayed as a solid icon (**{attention-solid}**) on
+the merge request list page:
+
+![Attention request icon](img/attention_request_list_v14_10.png)
+
+To view a list of merge requests that need your attention:
+
+1. On the top bar, select **Merge requests**. (**{merge-request}**)
+1. Select **Attention requests**.
+
+To request attention from another user:
+
+1. Go to the merge request.
+1. On the right sidebar, identify the user you want to request attention from.
+1. Next to the user's name, select **Request attention**, and the appearance
+   of the icon changes:
+
+   ![Attention request toggle](img/attention_request_sidebar_v14_10.png)
+
+### Remove an attention request
+
+If your attention was requested as an assignee or reviewer, it's removed when you:
+
+- You manually remove the attention request by selecting **Remove attention request** (**{attention-solid}**).
+- Approve the merge request.
+- Add a new user as an assignee or reviewer.
+- Request the attention of a different assignee or reviewer.
+- Remove yourself (or are removed by someone else) as an assignee or reviewer.
+- Merge or close the merge request.
+- Manually remove the attention request by selecting **Remove attention request**. (**{attention-solid}**)
+
+If you are both the assignee and a reviewer on a merge request, you receive
+only one attention request, which is synced across both duties. If the
+attention request is removed from you, either as an assignee or a reviewer,
+it is removed from both your duties.
+
 ## Close a merge request
 
 If you decide to permanently stop work on a merge request,