Document the size limit on Cobertura XML files

doc/user/project/merge_requests/test_coverage_visualization.md

@@ -52,10 +52,15 @@ from any job in any stage in the pipeline. The coverage displays for each line:
 Hovering over the coverage bar provides further information, such as the number
 of times the line was checked by tests.
 
-NOTE:
+### Limits
+
 A limit of 100 `<source>` nodes for Cobertura format XML files applies. If your Cobertura report exceeds
 100 nodes, there can be mismatches or no matches in the merge request diff view.
 
+A single Cobertura XML file can be no more than 10MiB. For large projects, split the Cobertura XML into
+smaller files. See [this issue](https://gitlab.com/gitlab-org/gitlab/-/issues/328772) for more details.
+When submitting many files, it can take a few minutes for coverage to show on a merge request.
+
 ### Artifact expiration
 
 By default, the [pipeline artifact](../../../ci/pipelines/pipeline_artifacts.md#storage) used