docs(uib): add document viewer issue in FAQ (#2815)

Covers [PROD-336](https://bonitasoft.atlassian.net/browse/PROD-336)

[PROD-336]:
https://bonitasoft.atlassian.net/browse/PROD-336?atlOrigin=eyJpIjoiNWRkNTljNzYxNjVmNDY3MDlhMDU5Y2ZhYzA5YTRkZjUiLCJwIjoiZ2l0aHViLWNvbS1KU1cifQ

modules/applications/pages/ui-builder/faq.adoc

@@ -205,4 +205,17 @@ These errors are likely related to your Bonita server being down.
 
 [.solution]#Solution#
 Ensure that your Bonita server is active and running.
+--
+
+[#DocumentViewerissue]
+[.troubleshooting-section]
+--
+[.symptom]
+The Document Viewer widget doesn't seem to be functioning as expected. How can I view my documents?
+
+[.cause]#Cause#
+The `Document Viewer` widget currently doesn't support the Bonita Document viewer links (formsDocumentImage).
+
+[.solution]#Solution#
+You can use an `Iframe` widget as an alternative solution.
 --