Add docs for reviewer filtering

doc/user/search/index.md

@@ -118,6 +118,13 @@ the dropdown) **Approved-By** and select the user.
 
 ![Filter MRs by approved by](img/filter_approved_by_merge_requests_v13_0.png)
 
+### Filtering merge requests by reviewer **(CORE)**
+
+> [Introduced](https://gitlab.com/gitlab-org/gitlab/-/merge_requests/47605) in GitLab 13.7.
+
+To filter review requested merge requests for a specific individual, you can type (or select from
+the dropdown) **Reviewer** and select the user.
+
 ### Filtering merge requests by environment or deployment date **(CORE)**
 
 > [Introduced](https://gitlab.com/gitlab-org/gitlab/-/merge_requests/44041) in GitLab 13.6.