Add documentation for bulk editing of issues and merge requests

doc/user/project/bulk_editing.md

+# Bulk Editing
+
+>**Note:**
+- A permission level of `Reporter` or higher is required in order to manage
+issues.
+- A permission level of `Developer` or higher is required in order to manage
+merge requests.
+
+Fields across multiple issues or merge requests can be updated simutaneously by using the bulk edit feature.
+
+>**Note:**
+- Bulk editing of issues and merge requests is only available at the project level.
+
+To access the feature, navigate to either the issue or merge request list for the project and click 'Edit Issues' or 'Edit Merge Requests'. This will cause a sidebar to be shown on the right-hand side of the screen, where the available, editable fields are displayed. Checkboxes will also appear to the left-hand side of each issue or merge request, ready to be selected.
+
+Once all items have been selected, choose the appropriate fields and their values from the sidebar and click 'Update All' to apply these changes.
+

doc/user/project/issues/index.md

@@ -151,3 +151,7 @@ or Bugzilla.
 ### Issue's API
 
 Read through the [API documentation](../../../api/issues.md).
+
+### Bulk editing issues
+
+Find out about [bulk editing issues](../../project/bulk_editing.md).

doc/user/project/merge_requests/index.md

@@ -233,6 +233,10 @@ all your changes will be available to preview by anyone with the Review Apps lin
 
 [Read more about Review Apps.](../../../ci/review_apps/index.md)
 
+## Bulk editing merge requests
+
+Find out about [bulk editing merge requests](../../project/bulk_editing.md).
+
 ## Tips
 
 Here are some tips that will help you be more efficient with merge requests in