Adds known limitation when working with manifest lists

Author: Steven Smith

modules/images-imagestream-import-import-mode.adoc

@@ -5,7 +5,9 @@
 [id="images-imagestream-import-import-mode_{context}"]
 = Working with manifest lists
 
-You can import a single sub-manifest, or all manifests, of a manifest list when using `oc import-image` or `oc tag` CLI commands by adding the `--import-mode` flag. Refer to the commands below to create an image stream that includes a single sub-manifest or multi-architecture images.
+You can import a single sub-manifest, or all manifests, of a manifest list when using `oc import-image` or `oc tag` CLI commands by adding the `--import-mode` flag.
+
+Refer to the commands below to create an image stream that includes a single sub-manifest or multi-architecture images.
 
 .Procedure
 
@@ -40,4 +42,14 @@ $ oc import-image <multiarch-image-stream-tag>  --from=<registry>/<project_name>
 [NOTE]
 ====
 The `--import-mode=` default value is `Legacy`. Excluding this value, or failing to specify either `Legacy` or `PreserveOriginal`, imports a single sub-manifest. An invalid import mode returns the following error: `error: valid ImportMode values are Legacy or PreserveOriginal`.
-====
+====
+
+[discrete]
+[id="images-imagestream-import-import-mode-limitations"]
+== Limitations
+
+Working with manifest lists has the following limitations:
+
+* In some cases, users might want to use sub-manifests directly. When `oc adm prune images` is run, or the `CronJob` pruner runs, they cannot detect when a sub-manifest list is used. As a result, an administrator using `oc adm prune images`, or the `CronJob` pruner, might delete entire manifest lists, including sub-manifests.
++
+To avoid this limitation, you can use the manifest list by tag or by digest instead.