Clarification on indexing modes above screenshot.

We have experienced confusion related to setting of customer_grid indexer. Adding clarification above screenshot.
Also screenshot needs to be updated if magento/magento2#34557 is merged.

Author: bjornmeat

src/guides/v2.4/extension-dev-guide/indexing.md

@@ -140,10 +140,12 @@ To set these options:
 
 You can also reindex from the [command line]({{ page.baseurl }}/config-guide/cli/config-cli-subcommands-index.html#configure-indexers)
 
-The following figure shows an example of setting indexers to Update by Schedule:
+The following figure shows an example of setting indexers to Update by Schedule (Please note that the Customer Grid is not supporting Update by Schedule, as stated above):
 
 ![Changing indexer modes]({{ site.baseurl }}/common/images/index_index-modes.png){:width="600px"}
 
+
+
 ### Mview {#m2devgde-mview}
 
 The `mview.xml` file is used to track database changes for a certain entity.